Remember the post where I wondered If Milk Builds Strong Bones, Why Do People In Countries Who Consume The Most Have Higher Fracture Rates? I posted two maps, one of global milk consumption, another of global hip fracture rates. They clearly show a link between high milk consumption and increased bone fractures, as contradictory as that sounds. But my post wasn’t scientific. It was just raw, unadjusted data. Who knows if something other than milk was causing the fractures?
Well, the researchers in this next study wanted to know. They set out to examine the relationship between milk intake and fracture rates, as well as milk’s effect on mortality. Their data was adjusted for possible confounders including “age, total energy intake, body mass index, height, educational level, living alone, calcium supplementation, vitamin D supplementation, ever use of cortisone, healthy dietary pattern, physical activity, smoking status.”
Milk intake and risk of mortality and fractures in women and men: cohort studies, British Medical Journal, 28 October 2014
The researchers analyzed data from two large Swedish cohorts, one with over 61,000 women, another with over 45,000 men, during the course of 11 (for men) to 20 (for women) years.
“In women the adjusted mortality hazard ratio for three or more glasses of milk a day compared with less than one glass a day was 1.93.”
So, drinking 3 glasses of milk almost doubled women’s risk of death in that 20 years. Drinking milk also increased inflammation:
“A positive association was seen between milk intake and both urine 8-iso-PGF2α (a biomarker of oxidative stress) and serum interleukin 6 (a main inflammatory biomarker).”
“Our results may question the validity of recommendations to consume high amounts of milk to prevent fragility fractures.”
Some numbers… Among women, they “observed a positive association between milk intake and total mortality as well as fracture, especially hip fracture”:
For each glass of milk:
- A 15% increased risk of dying from any cause.
- A 15% increased risk of dying from cardiovascular disease.
For 3 or more glasses of milk compared to less than 1:
- A 93% increased risk of death from any cause.
- A 44% increased risk of death from cancer.
- A 60% increased risk for hip fracture.
The mechanism they proposed for these increased risks is something I’m not familiar with … galactose. Galactose is a sugar. It’s one of the two sugars that make up the disaccharide lactose, or milk sugar. (The other is glucose.) Here’s what they say:
“A high intake of milk might, however, have undesirable effects, because milk is the main dietary source of D-galactose. Experimental evidence in several animal species indicates that chronic exposure to D-galactose is deleterious to health and the addition of D-galactose by injections or in the diet is an established animal model of aging. Even a low dose of D-galactose induces 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 subcutaneous dose of 100 mg/kg D-galactose accelerates senescence in mice. This is equivalent to 6-10 g in humans, corresponding to 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 is not only a pathogenetic mechanism of cardiovascular disease and cancer in humans but also a mechanism of age related bone loss and sarcopenia.”
Milk is the primary source of galactose in humans’ diet. Milk that has been fermented or exposed to the action of bacteria (e.g cheese) contains less galactose because the bacteria consume it. Low-fat milk has proportionately more galactose than full-fat milk.
The BMJ is not a fringe journal. This study had to withstand rigorous peer review before it was published. And it isn’t the first study to uncouple the supposed positive link between dairy food and bone health. People who continue to advise consumption of 3 or more servings of dairy food a day to promote strong bones and reduce fracture rates are not keeping company with science. Who are they keeping company with?