Why Active Girls Need More Vitamin D
It is not enough for active girls to just take dairy products and calcium to maintain healthy bones, according to a study on stress fracture among adolescent girls. More vitamin D may more beneficial reported the researchers.
Kendrin Sonneville from the Children’s Hospital Boston stated that there was a reduction of the stress fracture risk by half among girls who had the highest intake of vitamin D and the effect was strongest when the girls had at least an hour of high-impact exercise each day.
In a separate study published on the Archives of Pediatrics and Adolescent Medicine, the intake of dairy products and calcium had no significant impact on the stress fracture risk among girls.
For a long time, nutrition experts have recommended the consumption of calcium from dairy products for bone health.
Having very low calcium is not good for the bones, so the stress fracture study is not actually disregarding the importance of calcium.
What it really does, along with the other prospective studies, is suggest that going a little beyond the minimum threshold of calcium intake is not enough to improve bone health.
But the study on vitamin D tells us that an extra dose of this vitamin can go a long way, especially that vitamin D deficiency is common among the adolescents.
Having something that can benefit your bone early in life can bring long-term benefits to your bone health, even when fracture risk and osteoporosis occur later in life.
Adolescents need to engage in weight-bearing activities to boost bone mass during this critical time of bone building. This, however, must not be excessive to the point that the bones become injured and cannot heal because of overuse or stress.
The Study Test and Results
The Growing Up Today Study involved 6,712 adolescent girls aged 9 to 15, who were monitored for seven years. The study found that 4 percent of the girls had stress fractures.
Then 90 percent of those who had stress fractures, 30 percent were engaged in sports or some sort of high-impact activity for one hour everyday.
Calcium or dairy intake does not lessen stress fracture risk
The mean calcium intake of the girls was 1,182 milligrams per day, which did not meet the 1,300 milligram recommended intake. Nevertheless, both high and low intakes were likely to develop a stress fracture just the same.
Differences in dairy intake did not show any significant benefit as well. The girls who had 3 or more servings of dairy per day did not have a lower risk of developing a stress fracture than those who did not take any dairy.
Vitamin D helps lessen stress fracture risk
As for the daily vitamin D intake, the girls averaged 376 international units or IU, which was below the recommended intake of 600 IU. Nevertheless, the girls who had more vitamin D intake had less risk of stress fracture.
The girls who had an intermediate intake of vitamin D averaging 450 IU a day had a 25 percent less risk of stress fracture compared to the girls who had the lowest vitamin D intake of 100 IU a day.
The girls who had gone a little above the recommended vitamin D inake of 663 IU a day, were the least likely to have a stress fracture compared to the group that had the least vitamin D intake.
Among the girls who spend an hour of high-impact exercise a day, the ones with the most vitamin D intake were 52 percent less likely to have stress fracture than the ones with the least vitamin D intake.
Recommendation for more research
The researchers did not see any impact of dairy intake on fracture risk, but they were surprised to find that high calcium intake actually increased the fracture risk among highly active girls. This is an area that still needs further research.
There are certain limitations in the conduct of this study. The biggest was the non-availability of serum vitamin D status data. Another limitation is the insufficient representation of the study sample. There were less socioeconomically diadvantaged girls that participated.
Lastly, vitamin D supplementation was not common at the time this study was conducted. So, a research on the protective effect of vitamin D supplements versus vitamin D in the diet might be helpful.
Photo credits: By Jim Cianca – Own work, CC BY-SA 3.0