Many of us have probably heard that a diet rich in milk products helps lower the likelihood of osteoporotic fractures. Milk contains 18 of 22 essential nutrients, including calcium, phosphorus and vitamin D. Intestinal uptake of these nutrients is enhanced by the enzymatic capacity to digest lactose into D-glucose and D-galactose by mutation in the lactase gene. A recent article in BMJ examined whether high milk consumption is associated with mortality and fractures in women and men.
A high consumption of milk may have adverse effects since milk is the main dietary source of D-galactose. Experimental evidence in several animal species suggests that prolonged exposure to D-galactose is harmful and the addition of D-galactose by injections or in the diet. Even a low amount of D-galactose stimulates changes that resemble natural aging in animals, including shortened life span caused by oxidative stress damage, chronic inflammation, neurodegeneration, decreased immune response and gene transcriptional changes.
A dose of 100 mg/kg D-galactose accelerates aging in mice. This is equivalent to 6-10 g in humans, equaling 1-2 glasses of milk. Based on a concentration of lactose in cow’s milk of approximately 5%, one glass of milk comprises about 5 g of D-galactose. The increase of oxidative stress with aging and chronic low grade inflammation not only a aids in the production and development of cardiovascular disease and cancer in humans but also a mechanism of age related bone and muscle loss.
BMJ concluded that a high milk intake was linked with higher mortality in one group of women and in another group of men and with higher fracture incidence in women. Given the observational study designs a cautious interpretation of the results is suggested.
Source: BMJ 2014;349:g6015