Relationship of vitamin D and parathyroid hormone with obesity and body composition in African Americans

Summary Background Obesity disproportionately affects African Americans (AA) (especially women), and is linked to depressed 25‐hydroxyvitamin D (25‐OH D) and elevated parathyroid hormone (PTH). The relationship of 25‐OH D and PTH with body composition and size in AA is not well known. Objective To determine the relationship of 25‐OH D and PTH levels with body composition and anthropometric measures. Design A cross‐sectional study was conducted in 98 healthy, overweight, adult AA enrolled in an NIH/NIEHS‐sponsored weight loss/salt‐sensitivity trial. Measurements Multivariable linear regression analyses were used to explore the relationship of 25‐OH D and PTH with body composition, determined by dual‐energy X‐ray absorptiometry, and anthropometric measures. Body composition and size were contrasted across vitamin D/PTH groups using general linear models: (i) normal (25‐OH D >50 nmol/l, PTH ≤65 pg/ml), (ii) low 25‐OH D and normal PTH and (iii) low 25‐OH D and high PTH. Results Age, gender and season‐adjusted regression analyses showed that PTH was directly correlated with total (P = 0·02), truncal (P = 0·03) and extremity (P = 0·03) fat mass, while 25‐OH D was inversely related to truncal fat mass (P = 0·02). Total fat mass in groups 1–3, respectively, was 30·0, 34·0 and 37·4 kg (P = 0·008); truncal fat mass was 13·4, 15·9 and 17·6 kg (P = 0·006) and extremity fat mass was 15·8, 16·9 and 19·7 kg (P = 0·02). Lean mass did not differ across the three groups. Conclusions Our findings show that lower 25‐OH D and raised PTH are both correlated, though in opposite directions, with fat mass, fat distribution and anthropometric measures in adult AA.