Ovarian Cancer

Ovarian cancer

Ovarian cancer is the fourth most common cancer among women in the UK. Around 6,900 new cases are diagnosed each year (Cancer Research UK, 2006). The ovaries are two almond shaped organs located on either side of the uterus. They produce eggs and the reproductive hormones (oestrogen and progesterone). The cause of ovarian cancer is unknown however some risk factors have been identified. There may be an increased risk for this disease among women: over the age of 65; who have never been pregnant; who started having periods at an early age; who had their first child after the age of 30 or who go through the menopause after the age of 50. Furthermore, the prolonged use of fertility drugs might increase the risk of ovarian cancer (Cancer Research UK, 2006). Taking the combined contraceptive pill reduces the risk of ovarian cancer: the longer you take the pill, the more the risk is reduced (NHS Direct, 2006). Taken together, these risk factors suggest that hormonal factors are involved in the development of ovarian cancer although the precise mechanisms remain unclear. Additional risk factors include a genetic component; a small number of ovarian cancers (five to 10 per cent) are caused by an inherited faulty gene (NHS Direct, 2006). The use of talcum powder in feminine hygiene (direct application to the genital area) has also been implicated (Cramer et al., 1999).

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). More recently, 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 between 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 failed to show such a link. It was a stalemate with no clear conclusion (Larsson et al., 2005). 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 case-control studies which tends to be collected at the time of diagnosis.

In a 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.

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.