The sport of ultramarathon is one of the most equalizing with regard to gender in the athletic world, with women often beating men even among the elite. This equality with regard to performance, however, doesn’t extend to physiology. In ultra-distance running, as in any other sport, women are more susceptible than men to a number of conditions that relate to hormone levels. The low body fat of the female athlete reduces circulating estrogen, a female sex hormone, which in turn affects a number of other aspects of physiology. One of these is bone density, such that female athletes are much more prone than either men or sedentary women to osteoporosis (Lynch et al). This, in turn, increases the female athlete’s risk of a stress fracture over that of either men or sedentary women.
A recent study of female Navy recruits examined the effect of supplementing them with calcium (one of the major components of human bone) and vitamin D (required by the human body in order to take up calcium from the gut) on the incidence of stress fractures (Lappe et al). The study was a relatively strong one; over 5000 women participated, and they were randomized (randomly assigned to either receive supplementation or a placebo). The women supplemented with calcium and vitamin D had a 20% lower incidence of stress fracture than the placebo group.
The study authors suggested that, based upon their results, supplementation with calcium and vitamin D could have prevented 187 stress fractures among the 14,000 female Navy recruits in the Great Lakes area. Based upon the well established link between low body fat and osteoporosis (especially when coupled with the relatively low-for-body-weight caloric intake often observed in female athletes) and the results of this study, female distance runners may wish to consider discussing a calcium and vitamin D supplement with a healthcare professional. Such supplements are relatively low-cost, and, assuming proper dosing, are relatively low-risk. Further, benefits extend beyond the prevention of stress fractures during the running years, as calcium and vitamin D are critical to preventing osteoporosis-associated symptoms and fractures in old age.
Lappe et al. Calcium and vitamin d supplementation decreases incidence of stress fractures in female navy recruits. J Bone Miner Res. 2008 May;23(5):741-9.
Lynch et al. The female runner: gender specifics. Clin Sports Med. 2010 Jul;29(3):477-98.
Additionally, the large number of subjects in this study give this number very high statistical power. This means that we can be quite sure that calcium and vitamin D play an important role when it comes to the development of stress fractures, at least among female Navy recruits.