Milk consumption paradoxically linked to increased risk of fractures and mortality

1. Higher milk consumption was associated with higher rates of cardiovascular disease and cancer mortality as well as all-cause mortality in Swedish men and women.

2. Women consuming three of more glasses of milk per day had a 1.6-fold increased risk of hip fracture, a relationship that was not observed in men or with increased consumption of fermented milk products.

Evidence Rating Level: 2 (Good)

Study Rundown: Milk contains complete protein as well as the majority of essential nutrients. Its intake has been championed to decrease the risk of osteoporotic disease. However, milk is also the main dietary source of D-galactose, which has been shown in animal models to cause increased inflammation, shortened life spans, and overall aging. This study sought to determine whether milk consumption might paradoxically increase the risk of fractures and mortality. Among over 60,000 surveyed women in a Swedish cohort, milk consumption was associated with higher rates of fracture and death from all causes, cardiovascular disease, and cancer. Among over 40,000 surveyed men in the another Swedish cohort, higher milk consumption was also linked with increased mortality, but less strongly than for women. Men did have an increased risk of cardiovascular disease mortality with increased milk consumption but did not have increased risk of cancer mortality or fracture. Interestingly, fermented milk product intake (e.g. yogurt and cheese) did not affect mortality or fracture risk.

This study benefited from its population based prospective design, studying over 100,000 people with a large range of milk intakes. The study was thorough in determining outcomes and dietary intake by utilizing national healthcare registries and in-depth food questionnaires. Finally, the authors adjusted for several important covariates such as socioeconomic status, history of steroid use, and smoking. Regardless, the possibility of residual confounding and reverse causation cannot be completely ruled out. Furthermore, the study’s generalizability is limited as it included only Swedish patients. Other populations may have varying rates of lactose intolerance and milk consumption, as well as differing nutrient concentrations in the milk available to them. Overall, this study suggests that higher milk consumption in adults may not be linked to improved health outcomes; it may, in fact, be associated with increased mortality and fractures.

Click to read the study in the BMJ

Click to read an accompanying editorial in the BMJ

Relevant Reading: Milk intake and risk of hip fracture in men and women

In-Depth [prospective cohort]: This study investigated the association of milk intake with fracture and mortality risk in two large Swedish cohorts, of 61,433 women aged 39-74 years and 45,339 men aged 45-79 years. Patients from the Swedish Mammography Cohort were surveyed initially from 1987-90 and resurveyed in 1997. Patients from the Cohort of Swedish Men were surveyed in 1997. Outcomes were followed up until December 31, 2010. Higher rates of milk consumption were associated with higher rates of death from all causes in women (adjusted HR 1.15, CI_95% 1.13 -1.17, for each glass of milk) and in men (1.10, CI_95% 1.03 -1.17, for three or more glasses of milk a day compared with less than one glass a day). Higher rates of cardiovascular disease mortality were also found in both sexes. In addition, women had higher rates of cancer mortality (1.07, CI_95% 1.02-1.11, for each glass of milk) and overall fractures. The strongest association present for hip fractures in women who consumed three for more glasses of milk a day(1.60, CI_95% 1.39-1.84). Consumption of fermented milk products was not associated with increased mortality or fracture risk. Furthermore, the study found milk intake to be positively associated with inflammatory biomarkers, specifically 8-iso-PGF2α in both sexes and interleukin-6 in men.

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