Osteoporosis (meaning porous bones) is a condition that affects the bones, causing them to become weak and more likely to fracture. Although the whole skeleton is usually affected, fractures most commonly occur in the spine, wrist and hips (NHS Choices, 2012t). Osteoporosis is sometimes called the silent disease as there are often no symptoms until a fracture occurs.
Bones consist of a thick outer shell and a strong inner mesh filled with a protein called collagen, calcium salts and other minerals. Osteoporosis occurs when calcium is lost from the bones and they become more fragile and prone to fracture. This debilitating condition tends to occur mostly in postmenopausal women between 51 and 75 due to a lack of the hormone oestrogen, which helps to regulate the incorporation of calcium into the bones. It can occur earlier or later and not all women are at equal risk of developing osteoporosis. Around three million people in the UK are thought to have osteoporosis and there are over 250,000 fractures every year as a result. Although commonly associated with post-menopausal women, osteoporosis can also affect men, younger women and children (NHS Choices, 2012t). In the UK, one in two women and one in five men over the age of 50 will break a bone mainly because of poor bone health (National Osteoporosis Society, 2013).
Osteoporosis has been called the silent epidemic as the first sign some people experience is a fracture. In 2006, the dairy industry responded to this health scare by promoting milk, cheese and yogurt directly to teenage girls in an advertising campaign called Naturally Beautiful, run by the Milk Development Council with the support from the European Commission (MDC, 2005a). Since then, the promoting of cow’s milk and cheese to teenage girls for bone health has decreased. DairyCo now tends to focus more on promoting milk in schools by providing ‘educational resources’ and website material for schools as well as promoting dairy farming actively to the public through their consumer facing website as well as talking to the media (Dairy Co, 2013d). Most people know about osteoporosis and it is commonly assumed that dairy products can help protect against it. Indeed it is deeply entrenched in the British psyche that calcium from dairy sources is essential for good bone health. However, this association is more to do with successful marketing than scientific evidence.
In 2012, researchers from The WHO Collaborating Centre for Metabolic Bone Diseases, at the University of Sheffield Medical School in the UK published a review of hip fracture incidence and probability of fracture worldwide.
Figure 9.0 shows the hip fracture rates for women per 100,000 from a range of countries. The pattern for men was broadly similar to that for women. The authors of this review observed a greater than 10-fold variation in hip fracture risk between countries (Kanis et al., 2012). The high-risk countries extended from North Western Europe (Iceland, UK, Ireland, Denmark, Sweden and Norway) through central Europe (Belgium, Germany, Austria, Czech Republic, Slovakia, Hungary, Switzerland and Italy) to the south east (Greece, Slovenia) and onwards (to the Lebanon, Oman and Iran). Other high-risk countries for women were Hong Kong, Singapore, Malta and Taiwan. Notably, if ethnic-specific rates were considered in the US, then Hispanic, Asian and Black populations (often lactose intolerant and so non-milk consumers) would be described as low risk but Caucasian women were deemed to be at a high risk (this is why the US appears in the middle of the graph). Regions of moderate risk included Oceania (a region centred on the islands of the tropical Pacific Ocean), the Russian Federation, the southern countries of Latin America and the countries of North America. Low-risk regions included the northern regions of Latin America, Africa, Jordan and Saudi Arabia, India, China, Indonesia and the Philippines. In Europe, the majority of countries were categorised at high or moderate risk with the exceptions of Croatia and Romania (Kanis et al., 2012).
In summary, fracture rates are highest in Caucasian women living in temperate climates and are somewhat lower in women from Mediterranean and Asian countries and are lowest among women in Africa. Countries in economic transition, such as Hong Kong, have seen significant increases in fracture rates in recent decades (WHO, 2003a). This indicates that environmental factors, such as diet, may be responsible. This view is supported by changes in risk in immigrant populations. For example, black Americans have a lower fracture risk than Caucasians in the US, but a much higher risk than black Africans. A similar scenario is seen among the Japanese population of Hawaii compared to those in Japan and Chinese people living in Singapore compared with mainland China (Kanis et al., 2012).
Many risk factors for osteoporosis have been identified including a low body mass index (BMI), low bone mineral density, reduced sunlight exposure (crucial for vitamin D production in the skin), early menopause, smoking, alcohol consumption and low physical activity levels. In addition, somewhat unexpectedly, obesity has been identified as a risk factor; so being underweight or overweight can increase the risk. Migration status obesity (whereby obesity levels among migrants are significantly higher compared with the native population as a result of increased availability of poor quality food and/or increased exposure to aggressive marketing of fast food), is also a risk factor (Kanis et al., 2012). Numerous dietary factors are thought to influence bone health and fracture risk, including: calcium, vitamin D, protein (including the ratio of plant to animal protein), potassium, sodium and fruit and vegetables (Appleby et al., 2007). Assessing the relative contribution of each of these is difficult as nutrients are not consumed in isolation and may work together or be influenced by other factors. Furthermore the experimental data is somewhat inconsistent with conflicting findings.
Figure 9.0 supports earlier research that shows how Western style diets accompany hip fracture rates around the world. There are a number of theories as to why this could be. One of the most popular - and controversial - is the acid-alkaline hypothesis.
The acid-alkaline hypothesis
The hypothesis that a high animal protein diet could be a risk factor for osteoporosis dates back to research conducted more than 40 years ago (Barzel and Jowsey, 1969). The hypothesis proposes that as food is digested, acids are released into the blood, and the body attempts to neutralise the acid by drawing calcium from the bones. This calcium is then excreted in the urine (the calciuric response). Animal proteins, from cow’s milk and dairy products, meat, fish and eggs, are said to have a particularly bad effect because of the greater amount of sulphur-containing amino acids they contain compared to most plant proteins. Sulphur-containing amino acids give rise to sulphuric acid when they are broken down in metabolism.
Modern diets in industrialised countries are considerably more acid-forming than the more alkalising foods that would have been consumed throughout the vast majority of human evolution. Just consider a beef-burger in a white bun with fries and a fizzy drink compared to nuts, seeds, fruit, leaves and water with the occasional piece of meat and/or fish… Consequently, it is suggested that humans may be poorly adapted to the contemporary acid-forming diets and that this may contribute to modern epidemics of chronic disease (Scialla and Anderson, 2013).
Until relatively recently, the acid-alkaline hypothesis has been widely accepted; in 2003, in their recommendations for preventing osteoporosis, the WHO stated that:
“With regard to calcium intakes to prevent osteoporosis, the Consultation referred to the recommendations of the Joint FAO/WHO Expert Consultation on Vitamin and Mineral Requirements in Human Nutrition which highlighted the calcium paradox. The paradox (that hip fracture rates are higher in developed countries where calcium intake is higher than in developing countries where calcium intake is lower) clearly calls for an explanation. To date, the accumulated data indicate that the adverse effect of protein, in particular animal (but not vegetable) protein, might outweigh the positive effect of calcium intake on calcium balance.” WHO, 2003a.
A substantial body of evidence links animal protein to a decrease in bone mineral density. A study, looking at hip fracture incidence in 33 different countries in relation to consumption of plant and animal protein, found that the countries with the lowest fracture rates also had the lowest intakes of animal protein. Conversely, in 10 of the 11 countries with the highest fracture rates, animal protein intake exceeded plant protein intake. The authors said that hip fracture incidence is directly related to animal protein intake and suggested that bone integrity is compromised by acid that results from the metabolism of animal proteins. They suggested that the moderation of animal food intake, coupled to an increased ratio of vegetable to animal food consumption, may confer a protective effect (Frassetto et al., 2000). Another study of 1,035 elderly women found that women with a high ratio of animal to vegetable protein intake had a greater risk of hip fracture than those with a low ratio (Sellmeyer et al., 2001). A further study of 757 young girls in urban Beijing in China, compared the effects of protein intakes from animal and plant sources on bone mass accrual over five years. Results showed that protein from animal foods, particularly meat, had negative effects on bone mineral content. It was concluded that higher protein intake, especially from animal foods, has a significant negative effect on bone mass accrual in pre-pubertal girls (Zhang et al., 2010).
Another study compared the effects of animal and plant protein in the diets of overweight and obese postmenopausal women dieting. They found that the energy-restricted diet with protein from meat sources promoted bone loss compared with an energy-restricted diet without meat. They concluded that for postmenopausal women, choosing a diet containing meat may decrease bone mineral density and increase the risk of osteoporosis (Campbell and Tang, 2010). This extends the findings of an earlier study which examined the levels of bone loss in 1,600 older women and found that vegetarians had lost only 18 per cent bone mineral compared to omnivores who had lost 35 per cent bone mineral by the age of 80 (Marsh et al., 1988).
Cross-cultural studies summarising data on protein intake and fracture rates from 16 countries compared industrialised and non-industrialised lifestyles and revealed strong links between a high animal protein diet, bone degeneration and the occurrence of hip fractures (Abelow et al., 1992). In the book The China Study, Campbell observed that in rural communities where animal protein made up just 10 per cent of the total protein intake (the other 90 per cent coming from plant-based sources) the bone fracture rate was one-fifth of that in the US where 50 per cent or more of total protein is made up of animal protein (Campbell and Campbell, 2005), again indicating a link between animal protein and bone degeneration. The traditional Inuit (or Eskimo) diet is made up almost entirely of animal protein. Inuits potentially have one of the highest calcium intakes in the world (up to 2,500 milligrams per day) depending on whether they eat whole fish, including the bones, or not. They also have a high rate of osteoporosis, even higher than white Americans (Mazess et al., 1974; Mazess et al., 1975; Pratt and Holloway, 2001).
A substantial body of evidence supports a positive link between fruit and vegetables and bone health. A review of the role of protein, calcium and bone health in women in the EPIC-Potsdam cohort in Germany found that vegetable protein played a positive role in maintaining good bone health (Weikhert et al., 2005). Indeed, vegetable consumption was found to be an independent negative predictor for the worldwide incidence of hip fracture and high consumption of fruit and vegetables was positively associated with bone mineral density in both women and men (Weikhert et al., 2005). The research showing that plant proteins confer a beneficial effect on bone health is consistent.
Other studies have investigated the effects of cow’s milk and calcium in relation to bone health. The Harvard Nurses’ Health study examined whether higher intakes of milk can reduce the risk of osteoporotic fractures. The study observed over 75,000 women for 12 years and concluded that increasing milk consumption did not confer a protective effect against hip or forearm fracture. In fact the 1997 study found that an increased calcium intake from dairy foods was associated with a higher risk of fracture. They concluded that their results do not support the hypothesis that higher consumption of milk or other food sources of calcium by adult women protects against hip or forearm fractures (Feskanich et al., 1997). In a 2003 follow-up of the Nurses’ Health Study, the increased risk associated with dairy was not reported but they still found that higher daily intakes of cow’s milk did not reduce the risk of hip fracture. In other words, there was still no evidence of a protective effect of dairy against fracture risk (Feskanich et al., 2003). Interestingly, a lower risk of hip fracture was found among those with higher vitamin D intakes.
In a more recent extensive review of studies looking at total calcium intake and hip fracture risk, results showed that in prospective cohort studies, calcium intake was not significantly associated with hip fracture risk in women or men. The pooled results from randomised controlled trials not only found no reduction in hip fracture risk with calcium supplementation but suggested an increased risk with calcium supplementation among men and women (Bischoff-Ferrari et al., 2007).
So, for children and adolescents, while an adequate intake of protein is necessary for good bone development and stability, some research suggests that large intakes of animal protein may counter this positive effect. In a study looking at long-term dietary protein intake, dietary acid load and bone status in children, it was concluded that the positive effect of protein could be negated, at least partly, by a high renal acid load. The authors say that their findings support the health benefit of a diet rich in alkali-yielding fruit and vegetables (which is in accordance with the 5-a-day campaign) and recommend an integrative approach saying that focusing on single nutrients is not sufficient (Alexy et al., 2005). Such evidence, plus other studies showing that an animal protein-based diet (with the same total quantity of protein as a vegetarian diet) confers an increased risk for uric acid stones (Breslau et al., 1988) have led some to suggest that the high calcium losses in the urine caused by animal protein may be a risk factor for the development of osteoporosis.
A number of studies, including observational epidemiology and some small clinical trials, have examined the role of the dietary acid load in people with chronic kidney disease. It has been suggested that the evidence largely supports the hypothesis of a direct relationship between a higher dietary acid load and chronic kidney disease progression, bone loss and sarcopenia (loss of skeletal muscle). However, due to a wide variety of techniques and terminology used to quantify the dietary acid load, this theory is not widely appreciated by nephrologists (Scialla and Anderson, 2013). A number of critical reviews of the acid-alkaline hypothesis have been published (Darling et al., 2009; Fenton et al., 2009; Fenton et al., 2011). These reviews argue that a causal association between dietary acid load and osteoporosis is not supported by the research and say that there is no evidence that an alkaline diet can protect bone health (Fenton et al., 2011).
One of the main criticisms is that if bone is the primary source of calcium from which diet-related acid is buffered, it is suggested that all the bone in the body would be dissolved in just a few years (Bonjour, 2005). It is also argued that homeostatic mechanisms (including renal acid excretion) would not permit a steady-state low-grade metabolic acidosis caused by a typical Western diet. In other words, the body has ways of redressing the balance when, for example, the diet increases the acid levels in the blood, and even small increases in acidity are countered by these mechanisms – that is the theory anyway. However, it has been demonstrated that a high dietary acid load, which lies within the ranges seen in a typical American or European diet, can increase the acidity of blood to detectable levels (Frassetto and Sebastian, 2013). So, on the one hand we are told that we can compensate for the acidifying effects of a high-protein diet, while on the other hand, the research shows that we may not be able to balance it out completely. It may be that the truth lies somewhere between these two apparently irreconcilable arguments.
Buffers are chemical substances that can minimise changes in a liquid when it becomes more acidic or alkaline. To maintain equilibrium whilst there is an increased amount of acid in the body, at least three compensatory physiological responses are activated: buffering from the bone (and so some degree skeletal muscle), increased ventilation to eliminate carbon dioxide, and in the kidney, bicarbonate is generated and reabsorbed into the blood while excess hydrogen ions are secreted into the urine. In healthy people, these buffering systems all have a tremendous capacity to maintain the blood pH (acidalkali balance) within a very narrow margin (Kerstetter, 2009). However, the major reservoir of alkali (in the form of alkaline salts of calcium) is the skeleton, which provides the buffer needed to maintain blood pH and plasma bicarbonate concentrations (Pizzorno et al., 2010). While kidney metabolism represents a major mechanism by which metabolic acid loads are handled by the body, if the kidneys are overwhelmed or compromised (kidney function declines with age), calcium from the bones may be called on to compensate for the increasingly acidic environment and an alkalising diet could help redress the balance (Dargent-Molina et al., 2008; Frassetto and Sebastian, 2013). So, under certain conditions, the acid-alkaline hypothesis may provide a plausible mechanism in which a plant-based diet, rich in fruit and vegetables, could help promote and preserve bone health. This may go some way in explaining the apparently contradictory evidence concerning animal protein and bone health.
The acid-alkaline hypothesis has also been challenged on the basis of a series of short-term experimental studies that suggest that high-protein diets are not harmful to bone health and might actually be beneficial by improving calcium absorption (Kerstetter et al., 2003). However, while high-protein diets may increase calcium absorption, they also increase calcium excretion in the urine. Therefore, the positive effects of protein intake on bone health may only be beneficial under conditions of adequate calcium intake (Mangano et al., 2014). Indeed, growing evidence suggests that calcium and protein may interact in terms of bone health and that the potential harmful effect of a high-protein intake may be compensated for by an adequate calcium intake (Weikert et al., 2005). If there is insufficient calcium in the diet to counter the calciuric effect, calcium may be lost from the bone.The generally accepted daily protein dietary allowance is 0.8g per kg of body weight. One study (of just 13 participants) compared a moderate animal protein intake to a high animal protein intake diet (1.0g per kg body weight compared to 2.1g per kg) and found with 800mg of calcium per day, all participants ended up in negative calcium balance (Kerstetter et al., 2005). This was not anticipated and the authors suggested that the level of dietary calcium was not enough to maintain calcium balance. However, because the extra urinary calcium lost in the high-protein diet was found to come from the diet (as opposed to the bone), the authors concluded that, at least in the short term, high-protein diets are not detrimental to bone. While, the increased urinary calcium produced by the high protein diet may reflect enhanced calcium absorption and not bone resorption, under both the moderate and high protein diets tested, the vast majority (over 90 per cent) of the calcium found in the urine still came from the bones. Adult bones constantly undergo remodelling through bone resorption by osteoclasts and bone formation by osteoblasts. In adults, almost the entire human skeleton may be remodelled over a 10-year cycle. While this study suggests that higher protein intakes may not be harmful in the short term, it should be remembered that they can lead to kidney problems and increased levels of IGF-1 which are linked to certain cancers (see below). The long-term impact of high-protein diets on bone health is still unclear and the relative contribution of calcium from the bone and/or diet to protein-induced calciuria remains controversial (Heaney, 2002).
Other studies suggest that high-protein diets may increase calcium absorption and help preserve bone mass by stimulating IGF-1, a potent bone growth stimulator (Tang, 2014; Mangano et al., 2014). However, as stated, increased IGF-1 levels are linked to an increased risk of certain cancers so high animal protein diets are therefore not desirable and should not be recommended (see IGF-1).
Results of observational epidemiological studies have not helped to clarify the nature of the effect of highprotein intakes on the skeleton (Dargent-Molina et al., 2008). Some studies show a positive association with bone mass, some show no association and some show a negative association. Even fewer studies have investigated the effect of protein intake on fracture risk. These too have yielded mixed results including a decreased risk of fracture with higher protein intake, and increased risk of fracture with higher protein and some studies identify proteins from animal sources as the key factor increasing fracture risk.
A further possible confounding factor is that it is commonly assumed that all animal proteins have a higher content of sulphur-containing amino acids than all plant proteins. However, this may not be entirely correct, some plant proteins (certain grains) may have a greater potential to produce more sulphuric acid than animal proteins (Massey, 2003). Medical professionals use milliequivalents (mEq) to measure electrolyte levels in body fluids. Table 3.0 shows the mEq of selected animal and plant foods and shows how some plant proteins may have a greater potential to produce more mEq of sulphuric acid per gram of protein than some animal proteins. For example, if protein comes from white rice it would have a mEq of 0.68 per gram of protein while protein from milk contains 0.55 mEq per gram of protein (Hoffman and Falvo, 2004).
As stated, this is a complex issue with a wide range of factors involved, not least the role of the kidney. It should be noted that people who consume a high-animal protein diet have an increased risk of kidney disease and continuing to consume high levels of meat, eggs and dairy foods may present a burden on an already overworked kidney (see Kidney Disease). It seems logical that the harder you make the kidneys work, the more likely they are to struggle to meet the challenge. There appears to be some consensus that in people with kidney disease or poor kidney function (resulting from aging), a high dietary acid load may result in acidosis which may then lead to bone and muscle loss. In a recent study looking at the effects of dietary acid load in chronic kidney disease it was concluded that in the setting of chronic kidney disease and aging, a higher dietary acid load (determined by the balance of acid-inducing foods such as meats, eggs, cheese and cereal grains against alkali-inducing foods such as fruits and vegetables) may result in low-grade, subclinical acidosis (Scialla and Anderson, 2013). The authors went on to say that in these circumstances, efforts to maintain stable blood pH and boost acid excretion from the kidney may lead to bone and muscle loss and further decline in kidney function, but that this may be mitigated by alkali. In summary, they say that studies with hard outcomes are needed to determine the degree of benefits of a foods-based approach to reducing the dietary acid load in patients with early to moderate chronic kidney disease.
The acid-alkaline hypothesis is a controversial area of research. Currently, data that support both the proponents and opponents of the acid-alkaline hypothesis exist (Frassetto and Sebastian, 2013). The pattern of incidence of osteoporosis around the world certainly suggests that some aspect of the typical Western lifestyle could be a significant contributing factor to bone loss. Furthermore, the evidence shows that animal protein can be harmful to bone health but clearly more research is required. In the meantime, it seems prudent to observe how the Western diet is accompanied by the so-called Western diseases including osteoporosis and limit, if not eliminate, all animal protein from the diet.
If simply consuming sufficient levels of calcium was the answer to preventing bone loss, then Northwest European countries like Denmark, Sweden and the UK, and the US would have the lowest fracture rates in the world. This is simply not the case; in fact they have the highest rates, a fact that is often overlooked by health professionals. In the UK, the estimated average requirement (EAR) for calcium, whereby 50 per cent of the population’s requirement is met, is set at 525mg per day. The recommended amount or reference nutrient intake (RNI), whereby 97.5 per cent of the population’s requirement is met, for calcium for adults is 700mg per day. The 2003 UK National Diet and Nutrition Survey found that the average calcium intake for men and women was 1,007mg and 777mg per day respectively (144 and 111 per cent of the RNI respectively). Younger adults tended to have lower intakes but these were still above the EAR of 525mg per day). Overall, men and women had significantly higher average daily intakes of calcium in the 2003 survey than in the 1986/87 Adults Survey (Henderson et al., 2003a). So while a relatively small number of people had intakes on the low side, generally, the level of calcium intake in the UK was good. If you are already getting enough calcium, just adding more isn’t going to be helpful. It could be that getting sufficient calcium isn’t the problem, but that holding on to it is. As stated, there are genetic and lifestyle factors that can cause calcium to be lost from the body.
It should be stated that very low calcium intakes have been linked to poor bone health. A large-scale EPIC-Oxford study found that women with a low calcium intake (less than 525mg per day) had an increased risk of bone fracture compared with women with a calcium intake of at least 1,200mg per day (Key et al., 2007). Another EPIC-Oxford study found that a higher fracture rate among vegans compared with meat-eaters was halved in magnitude by adjustment for energy and calcium intake and disappeared altogether when the analysis was restricted to subjects who consumed at least 525mg per day of calcium. In other words, there is no reason to believe that vegans who consume an adequate amount of calcium would have different bone fracture rates to vegetarians or meat-eaters. The authors concluded that an adequate calcium intake is essential for bone health, irrespective of dietary preferences (Appleby et al., 2007). In a more recent study, the average intake of calcium among a group of UK vegans was higher than in Appleby’s 2007 study; 456 mg per day compared to 232 mg per day for men and 226 mg per day for women (Clarys et al., 2014). So, some people are not getting enough calcium in the diet and more care needs to be taken. This does not mean we should consume dairy products, far from it, the healthiest sources of calcium are plant-based foods that do not contain the harmful components found in cow’s milk and dairy products. Furthermore, care should be taken not to consume too much calcium as high intakes may be linked to an increased risk of heart attack or stroke (Daly and Ebeling, 2010). The UK NHS suggests that taking 1,500mg or less a day is unlikely to cause any harm (NHS, 2012v).
The role calcium plays in bone health is the hook the dairy industry uses to encourage parents to feed their children increasing amounts of dairy products. We have been repeatedly sold the line that cow’s milk and dairy foods are the best source of calcium. However, while calcium remains important for bone health, it could be that focusing on achieving high levels of calcium (above recommended intakes) has little benefit and may even cause us to neglect other lifestyle factors that could offer greater benefits. A 2005 review on dairy products and bone health published in the official journal of the American Academy of Pediatrics concluded that there is very little evidence to support increasing the consumption of dairy products in children and young adults in order to promote bone health. This review examined the effects of dairy products and total dietary calcium on bone integrity in children and young adults and found that out of 37 studies, 27 showed no relationship between dairy or dietary calcium intake and measures of bone health. In the remaining studies the effects on bone health were either small or results were confounded by the fortification of milk with vitamin D (Lanou et al., 2005). Another meta-analysis of 19 studies involving 2,859 children, published in the British Medical Journal found that calcium supplementation in children was unlikely to decrease the risk of fracture in childhood or in later life (Winzenberg et al., 2006). In this analysis, there were few studies involving children with low intakes. It may be that, providing we get adequate calcium, supplementing the diet offers no benefit and may actually be detrimental.
This research strengthens previous evidence that extra calcium or and/or dairy products do not have a clinically relevant impact on bone health in youth. More recently, a prospective study involving 61,433 Swedish women followed over 19 years, investigated associations between the long-term dietary intake of calcium and risk of fracture and osteoporosis. The findings did show an association between very low dietary calcium intake and an increased risk of fractures but above the base level of 750mg, increased intakes of calcium were not associated with a reduction in risk of fracture or osteoporosis. In addition to that, the rate of hip fracture was actually increased in those with high dietary calcium intakes (Warensjö et al., 2011).
There are many factors linked to bone health that may be more important than calcium. For example, some studies show that exercise is the predominant lifestyle determinant of bone strength. When the bone density of 80 young women was monitored over a 10-year period, it showed that exercise was more important than calcium intake (Lloyd et al., 2004). In a group of older people, a 15-year investigation into whether low calcium intake was a risk factor for hip fractures concluded that cutting back on dairy did not increase the risk and that physical activity provided better protection (Wickham et al., 1989). The discovery of 18th-century human bones under a London church revealed that today’s women lose far more calcium than our ancestors (Lees et al., 1993). This may be attributed to the lower degree of physical activity undertaken today. This research supports an increasing amount of evidence that physical activity is a key factor in reducing osteoporosis risk.
Other studies suggest a detrimental effect of dietary salt (sodium chloride) on bone health. One study describes how a typical American diet contains amounts of sodium chloride far above evolutionary norms and potassium levels far below. This imbalance is thought to contribute to the acid producing effects of a typical Western diet. This may contribute to development of osteoporosis, kidney stones and other health problems. The authors point out how, after seven million years of hominid evolution, humans remain genetically adapted to the potassium-rich, sodium chloride-poor, alkali-producing diet of our ancestral hunter-gatherers . In other words, our bodies are not well-suited to an acid-producing diet. The shift to the contemporary diet occurred too recently for evolutionary forces to have had the opportunity tomake any changes in our metabolic machinery. However, they suggest that decreasing salt intake and increasing the intake of plant foods may not just help the aging skeleton but provide other potential health benefits as well (Frassetto et al., 2008).
Other studies suggest a positive role in bone health for vitamin K. A review of projects funded by the UK Food Standards Agency examined the potential benefits of fruit and vegetables, vitamin K, early-life nutrition and vitamin D on bone health. They reached two conclusions; firstly that a diet rich in fruit and vegetables might be beneficial to bone health and secondly that an increased consumption of vitamin K may also contribute to bone health. A major research gap they identified was the need to investigate vitamin D status in relation to bone health in different groups (Ashwell et al., 2008). A higher calcium intake is still the primary recommendation for the prevention of osteoporosis, and vitamin D deficiency is often overlooked. In a study of US adults, a large proportion of younger and older adults were found to be below the desirable vitamin D threshold, whereas calcium intakes seemed to be adequate in the majority of individuals. The authors concluded that the correction of vitamin D status is more important than increasing dietary calcium intake (Bischoff-Ferrari et al., 2009).
The idea that humans must suckle from cows for their entire lives in order to meet their calcium needs is clearly absurd. An increasing amount of evidence now shows that milk is not the best source of calcium at all and suggests that our bone health would benefit enormously if we switched to plant-based sources. Interestingly, the 2003 National Diet and Nutrition Survey showed that a large share of the calcium in our diets (over 50 per cent) comes from sources other than dairy foods (Henderson et al., 2003a). This is not surprising as most people in the world (over 70 per cent) obtain their calcium from plant-based sources rather than dairy products. Good plant-based sources of calcium include non-oxalate dark green leafy vegetables such as broccoli, kale, spring greens, cabbage, bok choy and watercress.
Also rich in calcium are dried fruits, such as figs and dates, nuts, particularly almonds and Brazil nuts, and seeds including sesame seeds and tahini (sesame seed paste) which contains a massive 680mg of calcium per 100g. Pulses including soya beans, kidney beans, chick peas, baked beans, broad beans, lentils, peas and calcium-set tofu (soya bean curd) provide a good source of calcium. A good additional source is calcium-enriched soya milk. Interestingly, the calcium in dairy products is not as well absorbed as that in many dark green leafy vegetables, for example, in one study, calcium absorbability from kale was demonstrated to be considerably higher than that from cow’s milk (Heaney and Weaver, 1990).
The interaction between calcium intake and physical activity, sun exposure/vitamin D, intake of vitamin K, sodium, protein and protective phytonutrients (soya compounds), needs to be considered before recommending increased calcium intake in countries with low fracture incidence (WHO, 2003a). In a paper in the British Medical Journal, Dr Amy Lanou suggests that it is time to revise our calcium recommendations for young people and change our assumptions about the role of calcium, milk and other dairy products in the bone health of children and adolescents. Lanou argues that while the policy experts work on revising recommendations, doctors and other health professionals should encourage children to spend time in active play or sports and to consume a nutritious diet built from whole foods from plant sources to achieve and maintain a healthy weight and provide an environment conducive to building strong bones (Lanou, 2006).
In summary, we know that high-protein diets increase calcium excretion but the effect of high-protein diets on calcium absorption is still unclear. High acid-forming diets tend to increase calcium excretion, whereas a more alkaline-forming diet (rich in fruit and vegetables) decreases calcium excretion. Therefore, if you eat a high-protein diet but do not have sufficient calcium, it stands to reason that, over time, you may lose calcium from your bones. You may be able to limit this loss by increasing the amount of alkaline-forming
foods (fruit and vegetables) in the diet and limiting, or eliminating all animal protein. Furthermore, research suggests that physical (especially weight-bearing) exercise is the most critical factor for maintaining healthy bones, followed by improving diet and lifestyle; this means eating plenty of fresh fruit and vegetables, and cutting down on caffeine and avoiding alcohol and smoking.
For more information see Viva!Health’s fully-referenced scientific report Break Free – How to Build Healthy Bones and What Really Matters in the Prevention of Osteoporosis and easy-to-read guide Building Bones for Life at: www.vegetarian.org.uk/campaigns/bones.