Written by: Sandeep Ravindran, Ph.D. | Issue # 71 | 2018
- Previous studies of the association between milk intake and hip fractures have not shown a clear benefit for milk consumption.
- A recent longitudinal study of a large cohort of 123,906 U.S. adults followed over 32 years finds that milk intake and total dairy food consumption were both associated with a lower risk of hip fractures in older U.S. adults.
- The benefits of milk were not explained by its calcium, vitamin D, or protein content, and more studies are required to figure out what components of milk help lower fracture risk.
Bone density decreases with age, leading to an increased risk of hip fractures. Milk is considered helpful for maintaining bone health due to its high calcium, protein, and its fortification with vitamin D, and the 2015 Dietary Guidelines for Americans recommends that adults consume two to three cups of milk or equivalent dairy foods per day to protect aging bones .
However, the association between milk intake and hip fractures is far from clear-cut. No intervention studies have been conducted where one group of participants are given milk and then their risk of hip fractures is compared with that of a control group not given milk. The studies conducted so far have been prospective cohort studies, which followed individuals over time and collected information about their milk intake and whether they have suffered hip fractures to examine whether there were any associations between them. These cohort studies and meta-analyses of these studies have generally not supported an inverse relationship between milk intake and hip fractures [2-8].
“Previous studies of milk and hip fracture have not shown a clear benefit from milk, yet U.S. guidelines continue to recommend milk consumption for older adults,” says Professor Diane Feskanich of Brigham and Women’s Hospital and Harvard Medical School. “More recently, a study done in Sweden found an increased risk of hip fracture with higher milk intake in women but not in men, which I found surprising,” she says.
The Swedish study examined two large cohorts and found that women had a significant 9% greater risk of hip fracture for every glass of milk consumed per day, whereas no association was observed for men .
“This prompted us to do a similar analysis in our male and female cohorts,” says Feskanich. “There are differences in dairy consumption and hip fracture rates between Sweden and the U.S. and we did not want to assume that the Swedish findings would apply universally,” she says.
In a new longitudinal study, Feskanich and her colleagues found that among a large cohort of U.S. men aged 50 or older and women past menopause, higher milk and dairy intake were associated with a reduced risk of hip fracture .
“The Swedish study had gotten a lot of attention when it showed that hip fracture risk increased with higher milk intake in women,” says Feskanich. “So, our finding of a decreased risk with higher milk intake in both men and women shows that the book is not yet closed on this topic,” she says.
The new study examined the association between the long-term consumption of milk and other dairy foods and the risk of hip fracture in two large U.S. cohorts, the Nurses’ Health Study (NHS) of women and the Health Professionals Follow-up Study (HPFS) of men. In these two cohorts, 80,600 postmenopausal women and 43,306 men over 50 years of age were followed for up to 32 years.
Feskanich and her colleagues previously reported no significant associations between milk consumption and hip fractures in the NHS and HPFS cohorts [6-8]. However, their new study had increased statistical power with additional years of follow-up and hip fracture cases compared with the previous studies, and also expanded the analysis to account for a variety of factors including sex, age, and other dietary intakes.
In the new study, the researchers found that each serving of milk per day was associated with a significant 8% lower risk of hip fracture in men and women combined . Higher total dairy food consumption, which consisted of milk, cheese, yogurt, cream, and ice cream, was associated with a significant 6% lower risk of hip fracture per daily serving of dairy foods in men and women. The data also suggested that higher cheese intake in women may contribute to a lower hip fracture risk, but the result was not statistically significant.
The study yielded some unexpected results. “Two things were surprising,” says Feskanich. “One was that the benefit of milk did not seem to be due to the calcium, vitamin D or protein content of the milk, i.e., when we added total calcium, vitamin D and protein intakes to our statistical models, we still found a lower risk of hip fracture with higher milk intake,” she says. “ Future research would be useful which can examine what it is in milk that may lower fracture risk,” says Feskanich.
“The other surprising thing we found was that the benefit from milk was mostly found in men and women with higher body mass index,” says Feskanich. “This was an ad-hoc analysis and needs to be examined and confirmed by others,” she says.
The study concludes that higher long-term milk consumption in older U.S. adults is associated with a lower risk of hip fracture, and this finding was not explained by the calcium, vitamin D, or protein content of milk. “I don’t think that a dietary recommendation can be made based solely on our research, but it does suggest that older adults may safely choose to include milk as part of their plan for bone health,” says Feskanich.
Further studies of milk consumption and hip fracture may also benefit from looking at a variety of populations. “Dietary recommendations may not be one-size-fits-all, and future research needs to target specific populations,” says Feskanich.
1. U.S. Department of Health and Human Services and U.S. Department of Agriculture. 2015–2020 Dietary Guidelines for Americans, 8th Edition. December 2015. Available at http://health.gov/dietaryguidelines/2015/guidelines/.
2. Kanis J.A., Johansson H., Oden A., De Laet C., Johnell O., Eisman J.A., Mc Closkey E., Mellstrom D., Pols H., Reeve J., Silman A., Tenenhouse A. A meta-analysis of milk intake and fracture risk: low utility for case finding. Osteoporos Int. 2005 Jul;16(7):799-804.
3. Bischoff-Ferrari H.A., Dawson-Hughes B., Baron J.A., Kanis J.A., Orav E.J., Staehelin H.B., Kiel D.P., Burckhardt P., Henschkowski J., Spiegelman D., Li R., Wong J.B., Feskanich D., Willett W.C. Milk intake and risk of hip fracture in men and women: a meta-analysis of prospective cohort studies. J Bone Miner Res. 2011 Apr;26(4):833-9.
4. Sahni S., Mangano K.M., Tucker K.L., Kiel D.P., Casey V.A., Hannan M.T. Protective association of milk intake on the risk of hip fracture: results from the Framingham Original Cohort. J Bone Miner Res. 2014 Aug;29(8):1756-62.
5. Michaëlsson K., Wolk A., Langenskiöld S., Basu S., Warensjö Lemming E., Melhus H., Byberg L. Milk intake and risk of mortality and fractures in women and men: cohort studies. BMJ. 2014 Oct 28;349:g6015.
6. Owusu W., Willett W.C., Feskanich D., Ascherio A., Spiegelman D., Colditz G.A. Calcium intake and the incidence of forearm and hip fractures among men. J Nutr. 1997 Sep;127(9):1782-7.
7. Feskanich D., Willett W.C., Stampfer M.J., Colditz G.A. Milk, dietary calcium, and bone fractures in women: a 12-year prospective study. Am J Public Health. 1997 Jun;87(6):992-7.
8. Feskanich D., Willett W.C., Colditz G.A. Calcium, vitamin D, milk consumption, and hip fractures: a prospective study among postmenopausal women. Am J Clin Nutr. 2003 Feb;77(2):504-11.
9. Feskanich D., Meyer H.E., Fung T.T., Bischoff-Ferrari H.A., Willett W.C. Milk and other dairy foods and risk of hip fracture in men and women. Osteoporos Int. 2017 Oct 27.