Vitamin D status and 5-year changes in urine albumin creatinine ratio and parathyroid hormone in a general population

Vitamin D is associated with cardiovascular disease and renal function but the mechanisms are as yet unexplained. Microalbuminuria is associated with a higher risk of kidney function loss, cardiovascular disease, and mortality. Parathyroid hormone is a predictor of cardiovascular mortality and negatively correlated with glomerular filtration rate. We investigated the association between vitamin D status and 5-year changes in urine albumin creatinine ratio (UACR) and parathyroid hormone (PTH). A random sample of 6,784 individuals aged 30-60 years from a general population participated in the Inter99 study in 1999-2001. Vitamin D (serum-25-hydroxyvitamin D) was measured at baseline by high-performance liquid chromatography. UACR and PTH were measured at baseline and follow-up. Increased UACR was defined as UACR > 4.0 mg/g reflecting the upper quartile at baseline. We included 4,330 individuals who participated at 5-year follow-up. In multivariable linear regression analysis, a 10-nmol/l higher baseline level of vitamin D was associated with a 5-year decrease in UACR by 0.92 % (95 % confidence interval, CI 0.13, 1.71). In multivariable logistic regression analysis, the odds ratio of developing increased UACR during follow-up was 0.96 (95 % CI 0.92, 0.98) per 10 nmol/l higher baseline vitamin D level. We found a significant inverse cross-sectional (p < 0.0001) but no prospective association (p = 0.6) between baseline vitamin D status and parathyroid hormone. We found low vitamin D status to be a predictor of long-term development of increased UACR. It remains to be proven whether vitamin D deficiency is a causal and reversible factor in the development of albuminuria.