Sex Differences of Vitamin D Status across BMI Classes: An Observational Prospective Cohort Study

Abstract

Growing evidence reported that vitamin D deficiency is a common finding in obesity. Vitamin D status also seems to be sex-related, although little is known regarding this association. Therefore, the aim of this study was to investigate the sex-related differences of serum 25OH vitamin D (25OHD) concentrations across body mass index (BMI) classes and, if there were any differences, whether they could be explained by sex-related differences in body composition. We enrolled 500 subjects (250 males, age 37.4 ± 11.8 years; 250 females, age 36.6 ± 11.8 years). Body composition was assessed by bioelectrical impedance analysis (BIA) phase-sensitive system. Serum 25OHD concentration was quantified by a direct, competitive chemiluminescence immunoassay. Vitamin D deficiency was defined as a serum 25OHD concentrations < 20 ng/mL (50 nmol/L). Stratifying the sample population according to sex and BMI categories, 25OHD concentrations were significantly higher in males compared to females in all BMI classes and decreased along with the increase of BMI values. Females with vitamin D deficiency had higher fat mass (FM) % compared to males with vitamin D deficiency. The 25OHD concentrations inversely correlated with FM % in both sexes. In a multiple regression analysis model, sex, FM %, and BMI were predictive factors of 25OHD concentration. In conclusion, our study suggests that 25OHD concentrations were lower in females than males across all BMI categories. Given the tight correlation between 25OHD concentrations and FM %, it can be hypothesized that the lower 25OHD concentrations in females than males can be explained by the fact that females have a higher amount of fat than males.Nutrients 2019, 11, 3034 2 of 12 coming from The National Health and Nutrition Examination Survey (NHANES) 2005 to 2006 provide information regarding the prevalence of vitamin D deficiency in people with obesity and at normal weight. The 2005 to 2006 NHANES included certain subgroups of the US population, including low-income persons, older adults aged 60 years or older, African Americans, and Mexican Americans, to provide a more in-depth snapshot of these population groups. A total of 12,862 individuals were sampled in the 2005 to 2006 NHANES. Among the sampled individuals, 10,348 (80.5%) participated in the interview and 8306 (65%) provided valid data on vitamin D measurement. The findings of this study reported that the prevalence of vitamin D deficiency (vitamin D concentration < 20 ng/mL) has been reported to be higher (53.8%) in subjects with obesity compared to normal weight (33%) [6]. Body fat may represent a reservoir for vitamin D storage, reducing its bioavailability [7]. An inverse correlation between serum 25OHD concentration and magnitude of weight loss in people with obesity after bariatric surgery confirms this theory [8]. Indeed, large accrual in adipose tissue depot implies that vitamin D3 could not be appropriately released into the general circulation to support serum 25OHD concentrations. However, the sequestration and the inappr...

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