It appears that there still are many conflicting views about the health benefits of cow’s milk and this is being perpetuated by many “health” advisors who tell the public that cow’s milk is only good for calves and the evil source of many an unexplained ailment!
Milk makes a very valuable contribution to a healthy diet as it contains all the macro-nutrients (protein, carbohydrates and fat). Milk protein has a high biological value because it contains the essential amino acids needed by the body. The carbohydrate, lactose, supplies energy and aids the absorption of calcium. Milk is considered by many national and international opinion-leaders in the bone field as the best source of calcium because of the high calcium content, the absence of factors that may influence the absorption (such as phytates and oxalates in bran and green, leafy vegetables) and the presence of lactose which aids in the absorption of calcium. Milk also contains significant amounts of minerals and trace-elements calcium, phosphate, magnesium and selenium and vitamins A, D and B (riboflavin and niacin) – needed for bone health as well as general health.
Milk and bone health
The two key nutrients to consider for bone health are the mineral calcium and vitamin D. Milk and other dairy foods are the most readily available sources of calcium in the diet. Dairy foods also have the additional advantage of being a good source of protein and other micro-nutrients. The importance of nutrition to bone health has been demonstrated in a number of research studies, in human subjects across the age range. Intervention trials (the gold standard in supplying scientific evidence), carried out over three years in children and adolescents have shown that supplementation with either calcium, dairy calcium-enriched foods, liquid milk, or calcium-enriched milk powder enhances the rate of bone mineral acquisition, compared with un-supplemented (placebo) control groups. In general, these trials increased the usual calcium intake of the supplemented children from about 600-800mg/day to around 1000-1300mg/day. Some retrospective observational studies suggested that adults who consumed milk regularly during childhood had a higher bone mass than those who did not. At the population level, it is estimated that a 10% increase in peak bone mass could reduce the risk of osteoporotic fractures during adult life by 50%.
In studies among adults, one three-year intervention study in healthy young women aged 30-42 years showed that supplementing the usual diet with dairy foods prevented bone loss in the spine. In post-menopausal women and the elderly, several intervention studies have shown that calcium or milk supplementation slows the rate of bone loss. In a study carried out in healthy, elderly women living in nursing homes, calcium (1200mg/day) and vitamin D (800IU/day) supplementation over 18months reduced the risk of hip fractures and other non-vertebral fractures. A similar intervention over three years of calcium (500mg/day) and vitamin D (700IU/day) was shown to reduce bone loss and the incidence of non-vertebral fractures in elderly men and women living at home and not in institutions. In comparative intervention studies, dairy food supplements and calcium supplements were equally effective in preserving hip-bone mass in postmenopausal women, although these studies were not designed to evaluate reductions in fracture rates.
Does the protein in milk cause calcium loss?
In the Framingham study, elderly men and women with lower total and animal protein intakes had greater rates of hip and spine bone loss than those consuming higher amounts of protein. There is also evidence that increasing protein intake has a favourable effect on bone mineral density in elderly men and women receiving calcium and vitamin D supplements, suggesting synergistic effects of these nutrients in improving skeletal health. Randomized clinical trials in elderly people with hip fractures have demonstrated the beneficial effects of giving protein supplements on the clinical outcomes following surgery to repair the fracture. Protein supplementation resulted in fewer deaths, shorter hospital stays and a greater likelihood to return to independent living. Despite this evidence, there has been speculation that a higher dietary intake of protein could have negative effects on calcium metabolism and could possibly induce bone-loss. This relates to the hypothesis that the ‘acid-base balance’ of the diet is a potential risk factor for osteoporosis and if a diet contains predominantly acidic foods (which include key protein sources) and does not contain sufficient alkali-rich basic foods (fruits and vegetables), the alkaline salts of the skeleton may be drawn on to buffer this effect and in the long term lead to bone loss. Although there is some evidence from observational studies that a more alkaline diet is beneficial to bone health in pre- and post-menopausal women, the theory has not been proven in more definitive clinical trials.
The majority of scientific evidence supports the beneficial effects of protein intake on bone health, and highlights the risks associated with protein insufficiency and malnutrition. Although protein is needed for healthy bones, it is recommended that you limit protein intake to 75 grams/day.
What if I am lactose intolerant?
Lactose intolerance needs to be diagnosed by a doctor by doing certain tests as the abdominal symptoms can be confused with other digestive disorders such as irritable bowel syndrome. Lactose intolerance is a potential risk factor for osteoporosis as patients tend to avoid dairy products. Being lactose intolerant does not necessarily preclude all dairy products from the diet and some people can even tolerate small quantities of milk (< 12grams/meal) without symptoms. There are even some lactose reduced milks available. Fermented milk products like yoghurt can be well tolerated as the live cultures actually produce the enzyme lactase which helps in breaking down lactose to more digestible sugars glucose and galactose.
Dairy is good for you in more ways than one – being important in helping preserve bone mass and strength in the young and elderly, it speeds and aids healing time in those who have had a fracture and it helps prevent further fractures.