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High-dose, infrequent vitamin D supplementation reduces efficacy in older women
Older women randomly assigned high doses of vitamin D every 3 months did not maintain stable 25-hydroxyvitamin D levels for 1 year when compared with those randomly assigned a placebo, according to research in Clinical Endocrinology.
Ville-Valtteri Välimäki, MD, PhD, of Helsinki University Central Hospital in Finland, and colleagues analyzed data from 60 white women, all living in southern Finland, participating in a larger lifestyle intervention study aimed at preventing hip fractures (mean age, 75 years). Researchers randomly assigned 5 mL (n = 20; 100,000 IU) or 10 mL (n = 20; 200,000 IU) oral cholecalciferol together with 5 mL of olive oil, or 10 mL olive oil alone (placebo; n = 20) every 3 months, along with 500 mg oral calcium twice daily. Blood and 24-hour urine samples were collected at baseline, 3, 6, 9, 10 and 12 months, and 1 week after each vitamin D administration.
Researchers analyzed serum calcium, serum 25-(OH)D, 1,25-(OH)2D, parathyroid hormone, creatinine, type 1 procollagen amino-terminal propeptide, type 1 collagen C-terminal telopeptide and sclerostin. Participants completed a questionnaire at baseline, 6 and 12 months to assess dietary intake of vitamin D and calcium. Baseline vitamin D levels were similar across the three treatment groups (mean baseline serum 25-(OH)D levels, 59 nmol/L for 100,000-IU group, 64 nmol/L for 200,000-IU group and 61 nmol/L for placebo group). Primary endpoint was the percentage of serum 25-(OH)D measurements reaching or exceeding targets of 75 nmol/L or 50 nmol/L after baseline in each of the three groups.
Researchers found that, although serum 25-(OH)D levels increased in both vitamin D groups when compared with placebo, the difference between the two doses was of borderline significance (P = .0554; area under curve [AUC] analysis). The 200,000-IU group saw immediate, post-administrative higher vitamin D levels at 3- and 6-month dosing when compared with the 100,000-IU group (P < .05). In both vitamin D groups, only 51.2% of the 100,000-IU group and 57.7% of the 200,000-IU group reached the target level of 75 nmol/L.
Researchers found marginal between-group differences in parathyroid hormone levels (P = .0759), attributed to the tendency to lowering immediately after vitamin D boluses; urinary calcium differed between the groups (P = .0193) due to increases 1 week after vitamin D dosing. Bone turnover markers did not differ between study groups, although all declined during the study period (P < .001).
“Surprisingly, by AUC analysis, there was only a borderline difference in 25-(OH)D levels between the two vitamin D groups, despite doubling the dose,” the researchers wrote. “Thus, it seems that to improve the results of intermittent, high-dose vitamin D therapy ... instead of increasing the dose, the dosing interval has to be further shortened.” – by Regina Schaffer
Disclosure: The researchers report no relevant financial disclosures.