The association between serum 25-hydroxyvitamin D₃ concentration and risk of disease death in men: modification by magnesium intake

Low vitamin D status increases the risk of death. Magnesium plays an essential role in vitamin D metabolism and low magnesium intake may predispose to vitamin D deficiency and potentiate the health problems. We investigated whether magnesium intake modifies the serum 25(OH)D₃ concentration and its associations with mortality in middle-aged and older men. We included 1892 men aged 42–60 years without cardiovascular disease or cancer at baseline in 1984–1989 from the prospective, population-based Kuopio Ischaemic Heart Disease Risk Factor Study. Serum 25(OH)D₃ was measured with the high-performance liquid chromatography using coulometric electrode array detection. Magnesium intake was assessed with 4-day food recording. Deaths were ascertained by a computer linkage to the national cause of death register. Deaths due accidents and suicides were excluded. Cox proportional hazards regression models were used to analyze the associations. The multivariate-adjusted hazard ratio (HR) for death in the lowest (<32.1 nmol/L) versus the highest (>49.4 nmol/L) serum 25(OH)D₃ tertile was 1.31 (95 % CI 1.07–1.60, P_trend = 0.01). Stratified by the magnesium intake, the higher risk was observed only in the lower magnesium intake median (<414 mg/day); HR = 1.60 (95 % CI 1.19–2.13, P_trend = 0.002) in the lowest versus the highest 25(OH)D₃ tertile, whereas the corresponding HR = 1.07, 95 % CI 0.75–1.36, P_trend = 0.63) in the higher magnesium intake median, P for interaction = 0.08. In this cohort of middle-aged and older men low serum 25(OH)D₃ concentration was associated with increased risk of death mainly in those with lower magnesium intake.