The ovaries are two almond shaped organs located on either side of the uterus. They produce eggs and the reproductive hormones (oestrogen and progesterone). Ovarian cancer affects more than 6,500 women in the UK each year. It is the fifth most common cancer among women after breast cancer, bowel cancer, lung cancer and cancer of the uterus (NHS Choices, 2012f).
Several possible risk factors for ovarian cancer have been identified. Most ovarian cancers are due to gene changes that develop during a woman’s life but about one in 10 ovarian cancers are caused by an inherited faulty gene. Faulty inherited genes that increase the risk of ovarian cancer include BRCA1 and BRCA2; these genes also increase the risk of breast cancer (Cancer Research UK, 2012a). As with most cancers, the risk of developing ovarian cancer increases as you get older. Most cases are in women who have had their menopause.
Apart from getting older, the risk of ovarian cancer may be increased by a range of actors including:
- A family history of cancer
- Having breast cancer
- Being infertile or having fertility treatment
- Using a coil (intra uterine device – IUD)
- Using hormone replacement therapy (HRT)
- Being overweight or tall
- Having endometriosis
- Using talcum powder
- Diet factors
Source: Cancer Research UK, 2012a.
It has been suggested that the milk sugar lactose is a risk factor for ovarian cancer. A positive relationship between ovarian cancer and dairy products was first reported in the Lancet in 1989 when it was suggested that lactose consumption may be a dietary risk factor for ovarian cancer (Cramer et al., 1989). In 2004, data collected from the Harvard Nurses’ Health Study was used to assess the lactose, milk and milk product consumption in relation to ovarian cancer risk in over 80,000 women. Over 16 years of follow-up, 301 cases of one particular type of ovarian cancer were confirmed in this study group. Results showed that women who consumed the most lactose had twice the risk of this type of ovarian cancer than women who drank the least lactose. It was suggested that galactose (a component of lactose) may damage ovarian cells making them more susceptible to cancer (Fairfield et al., 2004).
In the same year, Susanna Larsson and colleagues of the Karolinska Institute in Stockholm, Sweden, published a study in the American Journal of Clinical Nutrition that examined the association betwen intakes of dairy products and lactose and the risk of ovarian cancer. In this study of 61,084 women aged 38 to 76 years, the diet was assessed over three years and after 13.5 years 266 participants had been diagnosed with ovarian cancer. Results showed that women consuming four or more servings of dairy a day had double the risk of ovarian cancer compared to low or non-dairy consumers. Milk was the dairy product with the strongest positive association with ovarian cancer. The authors of this study observed a positive association between lactose intake and ovarian cancer risk and concluded that high intakes of lactose and dairy products, particularly milk, are associated with an increased risk of ovarian cancer (Larsson et al., 2004).
Larsson subsequently compared two groups of studies: three prospective cohort studies and 18 case-control studies. The results of the three prospective cohort studies showed a strong link between the intake of total dairy foods, low-fat milk and lactose and the risk of ovarian cancer. In contrast, the data from the 18 case-control studies produced mixed results and (except for whole milk, which was consistently linked to an increased risk of ovarian cancer) these studies did not provide evidence of a positive association between dairy food and lactose intake with ovarian cancer (Larsson et al., 2006). The differences between the findings of the cohort and case-control studies might be explained by a number of factors including selection bias (choosing individuals that are not representative of the norm) or changes in the diet following cancer diagnosis. Alternatively, the differences between the findings may be due to the time interval between diet assessment and cancer diagnosis. Cohort studies frequently record dietary practices many years before illness occurs, which may make the data more likely to be accurate compared to data collected in casecontrol studies which tends to be collected at the time of diagnosis.
In another study examining the link between diet and ovarian cancer, ovarian cancer incidence between 1993 and 1997 in different geographical locations was coupled to food consumption data from FAOSTAT Database Collections. The food items used for this study were animal fats, meat (beef, pork, poultry, mutton and goat meat), eggs, butter, milk, cereals, pulses, beans, soya beans, peas, fruits, vegetables, coffee, tea and alcoholic beverages. Results showed that Iceland had the highest rates of ovarian cancer affecting 16.2 women per 100,000, followed by 15.2 in Sweden and 13.7 in the UK. The lowest rate per 100,000 was 1.6 for Korea, followed by 2.1 in Mali and 4.0 in both China and Brazil. Again, results showed a strong link between dairy foods and cancer: milk was most closely correlated with the incidence of ovarian cancer, followed by animal fats and cheese. Conversely, pulses were negatively correlated with the incidence of this cancer (Ganmaa and Sato, 2005). This provides yet more evidence that animal-based foods tend to increase the risk of disease while whole grain plant-based diets reduce the risk.
While several other studies have shown that dairy intake increases ovarian cancer risk, other studies have found no evidence of an association. A number of epidemiological studies have also examined the influence of specific nutrients from dairy products, including lactose, calcium and fat in the development of ovarian cancer. However, results from these studies are also mixed. In an effort to resolve this uncertainty, scientists from The Danish Cancer Society Research Center investigated the association between intake of specific dairy products and related nutrients (lactose and calcium) and ovarian cancer risk in a large population-based case-control study among Danish women. They found that the intake of dairy products (particularly milk, soured milk products and yoghurt), was associated with an increased overall ovarian cancer risk. A similar association was found between lactose intake and overall ovarian cancer risk (Faber et al., 2012).
In conclusion, the consumption of animal-based foods is associated with an increased risk of certain hormone-dependent cancers. Milk and dairy products are of particular concern: as already stated, most milk drunk today is produced from pregnant cows, in which oestrogen and progesterone levels are markedly elevated (Ganmaa and Sato, 2005). While there are several candidate components of milk that may increase the risk of ovarian and other hormone-dependent cancers, the precise mechanisms underlying their action remain unclear. However, as milk and dairy products have been identified as a risk factor for ovarian cancer, it stands to reason that this particular risk can be reduced by switching to a plant-based diet that excludes all dairy products.