From an early age, many of us are told that drinking milk is the key to strong and healthy bones. But is there such a thing as drinking too much milk?
Study Challenges Conventional Wisdom
In 2014, an observational study generated buzz by suggesting that drinking too much milk can have unintended health consequences.1
The research, published in BMJ, assessed fracture and mortality risk in 2 Swedish cohorts: one with 61,433 women aged 39 to 74 and another with 45,339 men aged 45 to 79. Using a questionnaire, participants reported how frequently they consumed up to 96 foods and beverages including milk and other dairy products. Lifestyle information, height, and weight were taken into account, and national healthcare registers were used to track fracture and mortality rates.
Over the 20 years during which the women were tracked, 17,252 (28%) had sustained a fracture and 15,541 (25%) died. Women who consumed at least 3 glasses of milk per day had a higher risk of fracture and mortality compared with women who drank less than 1 glass per day.
Over the 11 years during which the men were followed, 5066 (11%) had sustained a fracture and 10,112 (22%) died. While less pronounced than the female group, men also had a higher mortality risk with increased milk consumption.
The researchers concluded that high milk intake was found to be associated with increased risk of fracture in women and greater risk of mortality in both sexes.
Questioning a Paradoxical Result
The research elicited a number of critiques. Among them was a response paper, “Confusing message about dairy from Sweden,” authored by Arne Astrup, MD, DMSc, and Ian Givens, professors at the University of Copenhagen. The professors questioned whether there is something unique about the health effects of dairy in the Swedish population. They also questioned the validity of self-reported information in population studies.1
Gail Cresci, PhD, RD, a researcher and dietitian at the Cleveland Clinic, pondered whether the study’s participants were lacking in vitamin D. “Calcium is linked with bone health, but vitamin D promotes calcium absorption and maintains adequate blood levels of calcium and phosphate to allow for normal bone mineralization.” She added that it’s unclear whether or not the milk in the study was fortified with vitamin D or if lack of sunlight could have contributed to a vitamin D deficiency.2
The authors of the study advised a “cautious interpretation” of the results. “Our present investigation should not be evaluated in isolation and its merit should be judged in light of other study findings.”1
A Preponderance of Evidence
It’s not entirely surprising that an observational study would provide an outlier result, as these studies are unable to prove cause and effect. Here’s what we know for sure: the vast majority of clinical studies show an association between high calcium intake and a reduced risk for osteoporosis across age groups.
- A randomized controlled study in the Journal of Pediatrics found that young girls with high calcium intake exhibited an increased rate of bone mineralization compared with control subjects.3
- A randomized, double-blind, placebo-controlled study in the American Journal of Clinical Nutrition showed that children accustomed to a low-calcium diet saw an increase in bone mineral status with increased calcium intake.4
- A randomized study in the Journal of Clinical Endocrinology and Metabolism found that dairy products helped slow vertebral bone loss in premenopausal women.5
- A randomized, placebo-controlled study in the Journal of Bone and Mineral Research showed that calcium supplementation and exercise reduced bone loss in postmenopausal women.6
- A randomized, placebo-controlled trial in the Journal of Clinical Endocrinology and Metabolism found that calcium supplementation prevented seasonal bone loss in elderly women.7
- A randomized, double-blind, placebo-controlled trial in the Journal of Bone and Mineral Research showed that elderly women experienced decreased bone loss with long-term administration of calcium supplements.8
While the cohort study was interesting and worth revisiting, it shouldn’t change long-held views on milk – and more broadly, calcium – and its role in the modern diet.
- Michaelsson K, Wolk A, Langenskiold S, et al. Milk intake and risk of mortality and fractures in women and men: cohort studies. BMJ. 2014;349:g6015.
- Can drinking too much milk make your bones more brittle? Cleveland Clinic. November 10, 2014. Accessed May 15, 2019.
- Chan GM, Hoffman K, McMurry M. Effects of dairy products on bone and body composition in pubertal girls. J Pediatr. 1995;126(4):551-556.
- Dibba B, Prentice A, Ceesay M, et al. Effect of calcium supplementation on bone mineral accretion in Gambian children accustomed to a low-calcium diet. Am J Clin Nutr. 2000;71(2):544-549.
- Baran D, Sorensen A, Grimes J, et al. Dietary modification with dairy products for preventing vertebral bone loss in premenopausal women: a three-year prospective study. J Clin Endocrinol Metab. 1990;70(1):264-270.
- Prince R, Devine A, Dick I, et al. The effects of calcium supplementation (milk powder or tablets) and exercise on bone density in postmenopausal women. J Bone Miner Res. 1995;10(7):1068-1075.
- Storm D, Eslin R, Porter ES, et al. Calcium supplementation prevents seasonal bone loss and changes in biochemical markers of bone turnover in elderly New England women: a randomized placebo-controlled trial. J Clin Endocrinol Metab. 1998;83(11):3817-3825.
- Riggs BL, O’Fallon WM, Muhs J, et al. Long-term effects of calcium supplementation on serum parathyroid hormone level, bone turnover, and bone loss in elderly women. J Bone Miner Res. 1998;13(2):168-174.