(NaturalNews) Along with obesity, poor physical fitness may also be a significant risk factor for vitamin D deficiency, according to a study conducted by Spanish researchers and published recently in QJM: An International Journal of Medicine.
The study was conducted on 470 European males and 536 females between the ages of 12.5 and 17.5 who were taking part in the Healthy Lifestyle in Europe by Nutrition in Adolescence (HELENA) study. Researchers found that adolescents who were both more physically fit and less obese (indicated by a lower body mass index, or BMI) had significantly higher blood concentrations of vitamin D than adolescents with a higher BMI and lower fitness.
Furthermore, the researchers found that overall body fat content was significantly linked to vitamin D deficiency. In males, vitamin D deficiency was correlated with adiposity as well as higher BMI, while in females it was correlated with low fat-free mass. The researchers also found sex-specific correlations between vitamin D and fitness. Among males, higher vitamin D concentration was correlated with higher maximum oxygen consumption; among females, it was correlated with handgrip strength.
The researchers concluded that better fitness and lower BMI should lead to improved vitamin D levels.
"Therapeutic interventions to correct the high rates of vitamin D deficiency in adolescents should consider physical fitness," they wrote.
Vitamin D only improves bone mass in physically fit
The study is only the most recent analysis of HELENA data by the Spanish research team. In a study published in the journal Osteoporosis International just last year, the researchers showed that vitamin D may only improve bone density in adolescents who are physically fit.
Researchers have long known that vitamin D plays a critical role in the formation and maintenance of healthy bones and teeth. Rickets, the most well-known symptom of vitamin D deficiency, leads to bone softening and deformity.
The researchers took measurements of vitamin D concentration, bone mineral density, calcium and vitamin D intake, and physical activity and fitness from 47 Spanish males and 53 females between the ages of 12.5 and 17.5. They found that even after adjusting for age, sex, lean mass, time of year and calcium intake, higher blood concentrations of vitamin D were correlated with higher leg and overall bone mineral concentrations - but only among participants who were physically active.
The study was unable to determine whether vitamin D was leading to improvement in bone mass among physically active adolescents, or whether it was physical activity leading to an improvement in bone mass among adolescents who had sufficient vitamin D levels.
Obesity causes vitamin D deficiency
While the HELENA studies have only been able to demonstrate correlations between vitamin D, obesity and physical activity, a study recently published in the journal PLOS Medicine proved for the first time that obesity is actually a cause of vitamin D deficiency and not the other way around.
The researchers examined the results of 21 prior studies into the connection between obesity, vitamin D status and genetic predispositions to both conditions. They found that while people with genetic predispositions to obesity were more likely to have vitamin D deficiency, people predisposed to vitamin D deficiency were not any more likely to be obese.
Reacting to the study, David Haslam of the UK's National Obesity Forum encouraged people to improve both their weight and vitamin D levels through a simple measure: Spending more time outside.
"This research is a reminder that physical activity, like walking the dog or going for a run out in the sunshine, shouldn't be forgotten and can help correct both weight and lack of vitamin D," he said.