Is there a relationship between body mass index and serum vitamin D levels?

To evaluate the relationship between vitamin D level and body mass index (BMI) among Saudi Arabian citizens.

Four hundred healthy individuals aged > or =25 years (200 males and 200 females) were included in this cross-sectional study. Subjects were recruited in the period between 1st February 2008 and 31st May 2008 from the medical staff and employees of King Fahd Hospital of the University, Al-Khobar, Kingdom of Saudi Arabia, and from patients attending the endocrinology, orthopedic, and infertility clinics at the same hospital. Clinical evaluation was carried out, and BMI was calculated. Serum 25 hydroxy vitamin D (25OHD), in addition to serum parathyroid hormone levels and calcium chemistry were measured for all subjects.

The mean age was 46.5 +/- 14.6 years for males, and 42.6 +/- 15.9 years for females (p=0.01). Mean BMI was similar in both genders, and the difference in the level of serum 25OHD just reached statistical significance (p=0.04). Male subjects with vitamin D deficiency were found to be older (p=0.03), and with higher BMI (p=0.01) compared to males with normal 25OHD. Although female subjects with hypovitaminosis D were also older than subjects with normal vitamin D level (p=0.01), BMI was significantly lower in females with vitamin D deficiency (p=0.001).

Obese males are at higher risk of having low 25OHD levels, while obesity in females appears to be protective against vitamin D deficiency in the population studied. We believe that obese male and thin female patients should be appropriately investigated, and treated for vitamin D deficiency.