After vitamins C and E which ruled the nutraceutical market in the past, vitamin D is the latest over the counter craze among people who believe it to be a magical cure for all illnesses. While some believe it to have a protective effect in certain conditions, many also think that it is a promotional gimmick by pharmaceutical companies to up their sales. Let us take a quick look at some of the studies conducted in the past one year.
Studies with positive results:
A subsample of 500 patients from the PORMETS cross-sectional study showed a negative association between serum 25-hydroxyvitamin levels and metabolic syndrome, blood pressure and triglycerides. According to a study published in JAHA, monthly high dose vitamin D supplementation for a year lowered central BP parameters among adults with deficiency but not in the total sample. An evaluation of a subset of patients from the FAITH study showed that vitamin D supplementation was associated with statistically significant but not clinically significant improvement in HRQOL. Changes in circulating microRNAs (reduced miR-7 and miR-192 & elevated miR-152) were observed after 4 months of vitamin D supplementation in 42 pre-diabetic persons. This reflects a beneficial metabolic response in persons with prediabetes. Supplementing breakfast with vitamin D and leucine-enriched whey protein for a period of 6 weeks stimulated postprandial muscle protein synthesis and increased muscle mass in 24 healthy older adults. A two year sub-study of a trial in 452 community resident older adults showed a 2% improvement in bone mineral density at spinal and femoral sites in those with 25-hydroxyvitamin D ≤ 30 nmol/L. A secondary analysis of data from the Women’s Health Initiative Calcium/Vitamin D trial (34763 older women) revealed protective association between modest supplementation and the risk of hematologic malignancy. The association was found to be more robust for lymphoid malignancies. A randomized double blind trial (ECSPLOIT-D) consisting of 35 patients suffering from heart failure and vitamin D deficiency concluded that correction of deficiency improved 6 minute walking time after 3 months. However it did not influence echocardiographic and hormonal changes. The ‘high vitamin D dose’ group of a randomized study consisting of 297 postmenopausal women reported lower severity of urine incontinence as compared to the ‘standard dose group’ after one year. A study conducted in elderly women showed no decrease in falls on low vitamin D doses, a significant decrease on medium doses 1600, 2400,3200 IU (p=0.020) and no decrease on high doses compared to placebo. Gender based differences in gene expression were observed with vitamin D supplementation in 94 patients who were randomized to receive either vitamin D or placebo. These genes were involved in interleukin signaling, oxidative stress response, apoptosis signaling and gonadotropin hormone receptor pathway. A 2 year follow-up of 409 older home dwelling women concluded that vitamin D supplementation was associated with less injurious falls.
Studies with negative results:
Vitamin D supplementation for a year in 230 postmenopausal women did not improve frequency or intensity of muscle cramps. 113 patients with bone fracture (including 100 with deficiency/insufficiency of vitamin D) were randomized to receive either vitamin D or placebo. The rate of union was found to be independent of vitamin D supplementation. Vitamin D had no significant effect on mean levels of blood pressure, heart rate, arterial stiffness, echocardiographic measures or plasma N-terminal prohormone of brain natriuretic peptide concentration at 12 months in 305 older people in the UK. No positive effect of vitamin D was observed in 18 patients suffering from Barrett’s esophagus after 12 weeks of supplementation. Vitamin D did not improve respiratory muscle strength, physical performance, 6-minute walking test results, handgrip strength, pulmonary function or quality of life in 50 patients who were randomized to receive either the vitamin or placebo for a duration of 6 months. Similarly no benefit was observed with vitamin D supplementation in patients suffering from depression (n=33) and mild psoriasis (n=65) in their respective trials.
The RDA for vitamin D is 600 IU for ages 1 to 70 years and 800 IU beyond that. Normal levels of vitamin D are essential for optimizing calcium absorption and maintenance of bone health. However, hypervitaminosis can lead to toxic effects such as renal calculi, weakness, nausea and vomiting. Most of the above studies too have shown a positive result only in those suffering from a deficiency or insufficiency of the vitamin. Hence, rational prescribing of vitamin D must be encouraged.