“The countries with the highest rates of osteoporosis are the ones where people drink the most milk and have the most calcium in their diets. The connection between calcium consumption and bone health is actually very weak, and the connection between dairy consumption and bone health is almost non-existent.”
– Amy Lanou Ph.D., nutrition director for the Physicians Committee for Responsible Medicine in Washington, D.C.
The Milk Myth
For years we have been brought up with the belief milk is a good source of calcium and that drinking it promotes the development of strong teeth and bones. However, research undertaken by a team of Swedish scientists shows a link between milk consumption with increased mortality, bone fractures and osteoporosis.
In women over 20 years, drinking more than 200g of milk daily (less than one glass) was linked to increased mortality. This increased risk ranged from 21% for one to two glasses to 93% for those consuming three or more. More than one glass a day was also linked to an increased risk of fractures in women.
Other scientific studies contradict the conventional wisdom that milk and dairy consumption help reduce osteoporotic fractures. Surprisingly, studies demonstrating that milk and dairy products actually fail to protect bones from fractures outnumber studies that prove otherwise.
Cumming and Klineberg report that:
“Consumption of dairy products, particularly at age 20 years, was associated with an increased risk of hip fracture in old age. (“Case-Control Study of Risk Factors for Hip Fractures in the Elderly”. American Journal of Epidemiology. Vol. 139, No. 5, 1994).
Also a 12 year long Harvard Nurses’ Health Study found that those who consumed the most calcium from dairy foods broke more bones than those who rarely drank milk. This is a broad study based on 77,761 women aged between 34 and 59 years of age.
In the authors’ own words:
“Data does not support the hypothesis that higher consumption of milk or other food sources of calcium by adult women protects against hip or forearm fractures.” (Source: Feskanich D, Willett WC, Stampfer MJ, Colditz GA. Milk, dietary calcium, and bone fractures in women: a 12-year prospective study. American Journal of Public Health. 1997).
Theory of Causality
Drinking excessive amounts of milk is believed to acidify the body’s natural blood pH, which in turn triggers a biological correction in order to protect the kidneys. As calcium is an alkaline mineral it is thought that the body sacrifices calcium from the bones to neutralise the rise in blood acidity. Calcium from the bones is then excreted in the urine and not recycled leaving a net calcium deficiency.
Milk also contains D-galactose, a type of sugar. Experimental evidence in animals has suggested D-galactose is associated with ageing and damage to tissues at a cellular level. Researchers say an injected dose of 100mg/kg of D-galactose has been shown to accelerate biological signs of ageing in mice, which is equivalent to 6 to 10g in humans, or the amount found in one to two glasses of milk.
Should we be drinking milk at all?
It may be unfair to label milk as the sole culprit for bone weakening. Calcium loss from the bones has been linked to high intakes of all animal protein, not just milk. By the age of 80, vegetarians tend to have lost less bone mineral compared to omnivores.
Research suggests that the more animal protein you eat, the higher your risk of hip fracture becomes. Cross-cultural studies show strong links between a high animal protein diet, bone degeneration, osteoporosis and the occurrence of hip fractures. In rural communities in China where most of the protein in the diet came from plant foods rather than animal foods, the fracture rate was one-fifth of that in the US.
All baby mammals start off drinking milk. A mother’s milk contains all the vitamins, nutrients and antibodies to give a baby the best start in life. However, as baby mammals grow they become intolerant to the lactose in milk and once weaned they never drink it again. Humans are the only exception within the mammal population that is able to consume milk into adulthood (although even some of us have a normal and natural lactose intolerance).
Also, each mammalian species has its own milk formula and cow’s milk is no exception. For example, cow’s milk contains on average three times the amount of protein than human milk, which is perfect for a baby bovine but arguably not so good for humans who require a different composition of nutrients.
Conclusions about Osteoporosis
It is impossible to isolate milk protein as solely responsible for causing osteoporosis. There are many other lifestyle variables that may have an influence and need to be taken into consideration.
Many things affect bone health and osteoporosis including genetics, physical activity, body weight, smoking (including exposure to second hand smoke), alcohol consumption, hormone levels, and medications. Therefore, if any of those risk factors are more common in countries that have higher dairy consumption, then the link between dairy and osteoporosis may be nothing more than a coincidence. However, these findings are interesting enough to make further studies into this topic viable, if not a priority.
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Three glasses of milk a day can lead to early death, warn scientists. – The Daily Telegraph, October 28 2014
High milk diet ‘may not cut risk of bone fractures’. – BBC News, October 29 2014
Milk might not be as good for us as we thought, study suggests. – The Independent, October 28 2014
Three glasses of milk a day linked to earlier death. – Daily Express, October 29 2014
Should we be worried about drinking milk? – The Guardian, 16 November 2016
Michaëlsson K, Wolk A, Langenskiöld S, et al. Milk intake and risk of mortality and fractures in women and men: cohort studies. British Medical Journal. Published online October 28 2014