In class and student clinic, some of the most common disagreements over what we should and should not be eating involve dairy. But is all dairy the same? Actually, a large study published in the British Medical Journal found that pasteurised, unfermented milk may increase the risk of fractures and death, especially in women, while yoghurt and cheese could have the opposite effects.
In this study, over 61,000 women aged 39-74 at the beginning of the study were followed for an average of 20 years, while over 45,000 men aged between 45 and 74 were followed for an average of 11 years. Dairy consumption, death rates, fracture rates, and the inflammation markers IL-6 and PGF-2 alpha were all compared and contrasted among the many thousands of participants.
For the women, drinking three or more glasses of milk a day was linked with a 93% increased risk of death, compared with those who drank one or less glasses of milk per day. The men showed only a 10% increased risk of dying, although they were followed for a much shorter length of time. Men also did not have an increased risk of bone or hip fractures. However, women drinking at least three glasses of milk daily had their risk of hip fracture increased by 60%, and their risk of general bone fractures was raised by 16%. The risk of cardiovascular disease in these women was up by over 90%, and their cancer incidence was up by 44%.
While many would stop there to panic about the harmful effects of milk and generalise it to all dairy, it was also found that cheese, yoghurt and fermented milk have protective effects. Women eating at least 60 grams of cheese every day reduced their risk of mortality by over 30%, and when the beneficial effects of the nutrients in cheese were not cancelled out, this shot up to 49%! Risk of death from cardiovascular disease dropped by 37-52%, and death from cancer dropped by 5-15% in these women. Additionally, bone fracture risk halved, and hip fracture risk decreased by 36%. As for men, mortality dropped by 14-18% overall, and cardiovascular mortality fell by 13-22%, but there was no significant protection against cancer. Men's fracture risk only fell by 23-25%. As for yoghurt and fermented milk, women who consumed at least 400 grams daily experienced a 14-38% reduced mortality risk, a 7-32% lower risk of cardiovascular death and a 19-25% reduced risk of dying from cancer. Hip fractures decreased by 30-51%. Among men, this decreased overall mortality by 10-17%, cardiovascular deaths by 10-16% and cancer deaths by 11-17%, with yoghurt-eating men having a 25% lower risk of hip fractures.
So why is there such a dramatic difference between milk and fermented dairy? Milk has higher amounts of galactose and lactose, which are broken down by the bacteria in foods such as yoghurt. Casein, a protein linked to food sensitivities and related problems, is also broken down during the fermentation process, while the probiotics may also balance out the effects of IGF-1, or break them down. The differences between men and women may indicate beneficial effects of fermented dairy, and harmful effects of milk, on certain hormonal pathways.