Objective: To evaluate the association between 25-hydroxyvitamin D [25(OH)D] and metabolic syndrome (MetS) in Chinese population. Research design and methods: Plasma 25(OH)D was measured in a cross-sectional sample of 1443 men and 1819 women aged 50-70 years from Beijing and Shanghai. MetS was defined according to the updated National Cholesterol Education Program Adult Treatment Panel III criteria for Asian Americans. Fasting plasma glucose, insulin, lipid profile, HbA1c and inflammatory markers were measured.

Results: The geometric mean of plasma 25(OH)D was 40.4 nmol/l and percentages of vitamin D deficiency [25(OH)D <50 nmol/l] and insufficiency (50 /=57.7 nmol/l), the odds ratio for MetS in the lowest quintile (/=24 kg/m(2)), but not in their normal weight counterparts (test for interaction: P = 0.0363 and 0.0187 for insulin and HOMA-IR, respectively).

Conclusions: Vitamin D deficiency is common in the middle-aged and elderly Chinese and low 25(OH)D level is significantly associated with increased risk of having MetS and insulin resistance. Prospective studies and randomized clinical trials are warranted to determine the role of 25(OH)D in the development of MetS and related metabolic diseases.