The influence of renal function on vitamin D metabolism in the very elderly

Hypovitaminosis D and chronic kidney disease (CKD) are highly prevalent in older adults. The factors correlating with 25-OH-vitamin D and PTH levels were analyzed in older adults with and without CKD.

We performed a cross-sectional analysis embedded within the BELFRAIL study.

A population-based prospective cohort study of the very elderly in Belgium.

325 participants, all aged 80 or older.

Time of year and LAPAQ score were used as proxies for sunshine exposure. Vitamin D3 supplementation, gender, institutionalisation, age, level of education, and serum calcium and phosphorus level were examined as possible confounders in the analyses.

There was no correlation between the presence of CKD and low 25-OH-vitamin D levels, but there was a significant (p<0.01) correlation between CKD and high PTH levels. Among the participants with a normal eGFR, the LAPACQ score, vitamin D supplementation, season, log PTH value and eGFR were correlated with log 25-OH-vitamin D levels. Among the participants with CKD, only vitamin D supplementation, log PTH levels and serum calcium levels were correlated with log 25-OH-vitamin D levels. Gender, log 25-OH-vitamin D values, serum calcium and phosphorus levels and eGFR were correlated with log PTH values in the patients with normal eGFR. Log 25-OH-vitamin D values, serum phosphorus levels, vitamin D supplementation (p=0.07), season (p=0.10) and eGFR were correlated with log PTH values in the patients with CKD.

Exposure to sunshine and an active lifestyle were correlated with higher 25-OH-vitamin D levels in older adults without CKD. The PTH level in patients with CKD may be influenced by the season.