Will Supplementing with Calcium Help You Avoid Stress Fractures

A healthy diet is important for a distance runner, and you probably already know the basics. Fruits, vegetables, and good sources of carbs and protein make up the core of what an athlete should be eating.

But this week, we’ll take a look at the role of calcium, one of the major minerals that comes along with a lot of healthy foods.

In runners, calcium plays an important role in strengthening and repairing the bones after long or hard run. Since it is the main constituent of bones, it would make logical sense if diminished calcium intake would increase the risk of bone injuries in runners.

To see if this hypothesis holds true, we’ll turn to the scientific literature.

Test results involving calcium and vitamin D supplements

The first study we’ll examine is a 2008 paper by Joan Lappe and coworkers at Creighton University. Lappe et al. randomly assigned 5200 volunteers, all of them female recruits in the Navy, into two groups:

The first received calcium and vitamin D supplements daily, to the tune of 200% of their recommended daily value for calcium and 150% for vitamin D

The other group received a placebo pill. Vitamin D was included in the supplementation program because it boosts calcium absorption.

At the end of the eight-week study, stress fractures had occurred in 172 subjects in the control group (on the placebo) but in only 138 subjects in the experimental group, a relative reduction of 20%.

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.

But what about in runners?

Unfortunately, there have not been any large-scale high-quality randomized studies like Joan Lappe’s. However, a 2007 article published by Jennifer Kelsey and collaborators at a range of medical schools across the country investigated the risk factors for stress fractures in female cross country runners.

Training as a risk factor for stress fractures?

Some 127 women were followed for one to two years and a range of variables were tracked. The 18 women that developed a stress fracture demonstrated the following history:

• Stress fractures
• Decreased bone density
• Younger age
• Irregular menstruation
• lower dietary calcium intake.

Interestingly, training-related factors like weekly mileage and training surface did not play a role in the development of stress fractures.

This indicates that intrinsic causes of stress fractures, like bone size, muscle strength, or diet, likely play a larger role than extrinsic factors like how far or how fast you typically run.

Does vitamin D help prevent stress fractures?

In a 2010 review study, Adam Tenforde and colleagues at Stanford University recommend consuming 1500mg or more of calcium every day to reduce the risk of stress fractures, both for female athletes and for female military recruits. This is 50% greater than the National Institute of Health’s recommended calcium intake for men and women aged 19-50.

While Lappe’s study provides some evidence that vitamin D supplementation is helpful as well, Tenforde et al. concede that evidence is lacking on whether vitamin D plays a role in preventing stress fractures.

The authors call for more research on the interplay between calcium, vitamin D, and stress fractures, as there is a critical lack of information when it comes to some important questions:

How does vitamin D affect bone health in athletes? Would calcium supplementation help men avoid stress fractures too? Does calcium intake impact bone health in adolescence, when the bones are growing larger and stronger rapidly?

These are all as of yet unanswered, but given the medical and financial incentives (Lappe et al. predicted that the Navy could have prevented 187 stress fractures had a supplementation program been implemented among all 14,000 female Navy recruits in the Great Lakes region), there are likely already studies underway investigating these very questions.

Recommendations

It’s probably too early to recommend that all runners take a calcium and/or vitamin D supplement.

But if you have a history of stress fractures, especially if you’re a woman, it might make sense to follow the protocol from Lappe et al.: taking a daily calcium and vitamin D supplement which provides 2000mg of calcium and 800 IU of vitamin D, representing 200% and 150% of your recommended daily intake for each, respectively.

• However, you should be aware that taking supplemental calcium (but not calcium from food) has been linked to developing kidney stones, as well as a modest increase in risk for heart disease in older men and women.

• Calcium plays an important role in bone health in active women, but the extent to which this extends to men and younger women remains unclear, as does the role of vitamin D.

• More research is needed, but so far, it seems that female runners can reduce their risk of a stress fracture through calcium (and possibly vitamin D) supplementation on a daily basis.