Low vitamin D leads to obesity

PEOPLE with low serum 25(OH)D levels have a greater risk of developing obesity, and in particular greater waist circumference, researchers warn.

A random sample of 2460 participants in Norway’s HUNT population health survey were tested for baseline vitamin D, BMI and waist circumference. 

After 11 years a consistent inverse association between baseline vitamin D levels and incident obesity was found, unaltered by season.

Even in those with baseline BMIs lower than 30, a vitamin D level less than 50 nmol/L was associated with a significantly increased odds ratio for incident obesity during follow-up.

“Our study... provided new evidence that lower 25(OH)D levels may contribute to new onset obesity in adults,” the researchers said.

“We also found that central obesity increased more rapidly than overall obesity (38% vs 15%).” 

Sydney endocrinologist Dr Tania Markovic, director of metabolism and obesity services at Royal Prince Alfred Hospital, suggested people with low vitamin D who became obese typically spent less time outside in the sun because they were less physically active and were often anxious about their appearance.

“Along with fasting glucose, lipids and liver function testing, a vitamin D level should be done… in people who are obese,” she said, adding treatment with supplements and sunlight may be necessary.

As vitamin D is fat soluble, people with obesity may need higher total levels to achieve normal circulating levels, with experimental studies suggesting 1,25(OH)2D modulates the distribution of fat, the researchers said, adding people low in vitamin D often had secondary hyperparathyroidism. 

They postulated a cycle whereby low vitamin D leads to obesity, which lowers vitamin D levels further, complicating obesity prevention and treatment. 

Am J Epidemiol 2012, online 6 Feb