Impact of gender on vitamin D deficiency in morbidly obese patients: a cross-sectional study

BACKGROUND/OBJECTIVE: Obesity is associated with vitamin D deficiency (25-hydroxyvitamin D (25(OH)D) <50 nmol/l). We aimed to examine the effect of gender on vitamin D status in severe obesity. SUBJECTS/METHODS: Cross-sectional study of 2026 morbidly obese patients examined consecutively at a tertiary care centre between November 2005 and June 2010. Serum 25(OH)D concentration and use of vitamin D supplements were registered in all patients. Total vitamin D intake (μg/day) was assessed in a subgroup of 154 patients using a validated food frequency questionnaire. RESULTS: The male (n=690) and female (n=1336) patients had a mean (s.d.) age of 45.0 (12.1) years and 42.2 (12.2) years (P<0.001), body mass index (BMI) of 44.6 (6.0) kg/m(2) and 44.3 (5.9) kg/m(2) (P=0.30) and waist circumference (WC) of 140 (13) cm and 127 (13) cm (P<0.001), respectively. Male patients had significantly lower mean 25(OH)D concentrations than female patients 50.0 (22.0) nmol/l versus 53.6 (22.4) nmol/l (P=0.001) and a higher rate of vitamin D deficiency (56% versus 47%; P<0.001). Obese men had significantly higher odds of vitamin D deficiency than women (odds ratio=1.41; 95% confidence interval: 1.17-1.70, P<0.001), also after adjustment for season, age, current smoking, intake of vitamin D supplements, BMI and WC (odds ratio=1.39; 95% confidence interval: 1.10-1.76). CONCLUSIONS: Morbidly obese Norwegian men seeking weight loss treatment have significantly higher odds of vitamin D deficiency than women. Monitoring of 25(OH)D concentrations in obese patients should therefore take gender into account.