Relationship between body fat distribution and vitamin D status among university employees at a private university in Lebanon : a cross-sectionals study

Abstract

Background: High prevalence of suboptimal vitamin D status has paralleled the obesity epidemic; thus there has been a growing scientific interest in understanding the relationship between serum vitamin D levels and adiposity. Given the 1) high prevalence of vitamin D deficiency in Lebanon 2) lack of evidence on the association between body fat distribution (BFD), particularly direct measures of BFD, and serum vitamin D levels 3) lack of simultaneous control for important confounding variables, including indices of body composition, our study is the first to explore the association between a direct measure of body fat distribution (upper-to-lower body fat ratio-ULBFR) and vitamin D status, independent of %BF. The aim of our study is to examine the independent associations between different body fat location measurements and suboptimal vitamin D levels. We hypothesize that there is an independent association between different measures of BFD, particularly, ULBFR, and suboptimal vitamin D status. Methods: A cross sectional study was conducted among employees at a private university in Lebanon (Notre Dame University-Louaize). Anthropometric data (waist circumference (WC), height and hip circumference) were collected using standardized techniques. Waist-to hip ratio (WHR) and waist-to-height ratio (WHtR) were calculated as the waist measurement divided by the hip measurement or height, respectively. Cutoff points of ≥ 102 cm for men and ≥ 88 for women, ≥ 0.9 for men and ≥ 0.85 for women, > 0.5 for men and women, were used to identify individuals with unhealthy WC, waist-to-hip ratio, and waist-to-height ratio respectively. Body weight and body composition variables (fat mass, trunk fat mass, fat mass in the right and left legs/right and left arms, body fat percentage (BFP), fat free mass, skeletal muscle mass and visceral fat area (VFA)) were measured using the bioelectrical impedance anlaysis machine (BIA)- ( InBody 720, Biospace, Seoul, Korea). ULBFR was calculated as: (trunk fat mass (kg)) / (fat mass in right/lefty legs (kg)). Stratified analyses by gender, with women also stratified by menopausal status, was performed. Men, premenopausal and postmenopausal women were divided into three groups according to the tertiles of 1) ULBFR level and 2) VFA level. Serum 25-hydroxyvitamin D levels were measured using ELIZA and vitamin D status was determined according to the US Endocrine Society guidelines (Vitamin D deficiency: 25(OH) D ≤20 ng/mL; vitamin D insufficiency: 25(OH)D > 21 - 29 ng/ml and vitamin D sufficiency as 25(OH)D ≥30ng/ml). Statistical analysis was done using SPSS version 22. Results: A total of 344 employees participated in the study. About 71% of the study participants were found to have suboptimal vitamin D status (69% M vs. 75% W, P>0.05). Among men (n=176), no significant associations were found between suboptimal vitamin D status and WC, WHR, WHtR, VFA and ULBFR. Among premenopausal women (n=146), significant associations were found between suboptimal vitamin D status and WC, WHR, VFA and ULBFR. Premenopausal women with unhealthy WC and WHR were found to have about 4.6 times higher odds of developing suboptimal vitamin D status than those with healthy WC and WHR, after controlling for confounders. In addition, premenopausal women whose visceral fat areas fell in the second, third tertiles/ upper-to-lower body fat ratios levels fell in the third tertile were found to have about 5, 9 times/4 times higher odds of developing suboptimal vitamin D status as compared to those whose visceral fat areas/ upper-to-lower body fat ratios fell in the first tertile, respectively, after controlling for confounders. It is worth mentioning that 1) the association pertaining to ULBFR was independent of BFP and 2) BFP was found to be not associated with suboptimal vitamin D status independent of upper-to-lower body fat ratio and the other confounding variables in the final model. Conclusion: Our study results revealed that an increased ULBFR in premenopausal women increases the odds of suboptimal vitamin D status, independent of BFP, indicating a possible complementary role of body fat distribution than body composition in determining vitamin D status. Dieticians should consider examining body fat distribution in addition to body composition to identify and refer those with increased odds of suboptimal vitamin D levels for measurement of their serum vitamin D levels.