Vitamin D Supplementation lowers Risk for Respiratory Tract Infections
Objectives To assess the overall effect of vitamin D supplementation on risk of acute respiratory tract infection, and to identify factors modifying this effect.
Design Systematic review and meta-analysis of individual participant data (IPD) from randomised controlled trials.
Data sources Medline, Embase, the Cochrane Central Register of Controlled Trials, Web of Science, ClinicalTrials.gov, and the International Standard Randomised Controlled Trials Number registry from inception to December 2015.
Eligibility criteria for study selection Randomised, double blind, placebo controlled trials of supplementation with vitamin D3 or vitamin D2 of any duration were eligible for inclusion if they had been approved by a research ethics committee and if data on incidence of acute respiratory tract infection were collected prospectively and prespecified as an efficacy outcome.
Results 25 eligible randomised controlled trials (total 11 321 participants, aged 0 to 95 years) were identified. IPD were obtained for 10 933 (96.6%) participants.
Vitamin D supplementation reduced the risk of acute respiratory tract infection among all participants (adjusted odds ratio 0.88, 95% confidence interval 0.81 to 0.96; P for heterogeneity <0.001). In subgroup analysis, protective effects were seen in those receiving daily or weekly vitamin D without additional bolus doses (adjusted odds ratio 0.81, 0.72 to 0.91) but not in those receiving one or more bolus doses (adjusted odds ratio 0.97, 0.86 to 1.10; P for interaction=0.05).
Among those receiving daily or weekly vitamin D, protective effects were stronger in those with baseline 25-hydroxyvitamin D levels <25 nmol/L (adjusted odds ratio 0.30, 0.17 to 0.53) than in those with baseline 25-hydroxyvitamin D levels ≥25 nmol/L (adjusted odds ratio 0.75, 0.60 to 0.95; P for interaction=0.006). Vitamin D did not influence the proportion of participants experiencing at least one serious adverse event (adjusted odds ratio 0.98, 0.80 to 1.20, P=0.83). The body of evidence contributing to these analyses was assessed as being of high quality.
Conclusions Vitamin D supplementation was safe and it protected against acute respiratory tract infection overall. Patients who were very vitamin D deficient and those not receiving bolus doses experienced the most benefit.
Systematic review registration PROSPERO CRD42014013953.
Time for more vitamin D: https://www.health.harvard.edu/staying-healthy/time-for-more-vitamin-d
Missing out on the “sunshine vitamin” has consequences for more than just bone health.
September brings the end of summer in the northern hemisphere and, for many of us, that means less time in the sun. The sun’s rays provide ultraviolet B (UVB) energy, and the skin uses it to start making vitamin D. (The skin actually produces a precursor that is converted into the active form of the vitamin by the liver and kidneys.)
Vitamin D is best known for its vital role in bone health. Without this “sunshine vitamin,” the body can’t absorb the calcium it ingests, so it steals calcium from bones, increasing the risk of osteoporosis and fractures. Vitamin D also helps maintain normal blood levels of phosphorus, another bone-building mineral.
Vitamin D would be essential if it did nothing else. But researchers have discovered that it’s active in many tissues and cells besides bone and controls an enormous number of genes, including some associated with cancers, autoimmune disease, and infection. Hardly a month goes by without news about the risks of vitamin D deficiency or about a potential role for the vitamin in warding off diseases, including breast cancer, multiple sclerosis, and even schizophrenia.
In June 2008, a study published in the Archives of Internal Medicine found that low blood levels of vitamin D were associated with a doubled risk of death overall and from cardiovascular causes in women and men (average age 62) referred to a cardiac center for coronary angiography. At a scientific meeting in May 2008, Canadian researchers reported that vitamin D deficiency was linked to poorer outcomes in women with breast cancer. And a large study of aging in the Netherlands published in the May 2008 issue of Archives of General Psychiatry found a relationship between vitamin D deficiency and depression in women and men ages 65 to 95.
The picture of vitamin D’s health benefits beyond bones has been drawn mainly from epidemiologic and observational investigations. The findings of such studies can suggest correlations between disease risk and certain factors — sun exposure or blood levels of vitamin D, for example — but they don’t prove cause and effect. Promising findings from observational studies don’t always pan out when put to the test in clinical trials. However, in one of the few randomized trials testing the effect of vitamin D supplements on cancer outcomes, postmenopausal women who took 1,100 international units (IU) of vitamin D plus 1,400 to 1,500 milligrams of calcium per day reduced their risk of developing non-skin cancers by 77% after four years, compared with a placebo and the same dose of calcium.
The 1,100 IU dose — nearly three times the 400 IU per day recommended in federal and other expert guidelines — was correlated with a 35% higher blood level of vitamin D, on average. In the only other randomized trial of vitamin D and cancer — part of the Women’s Health Initiative — researchers found no effect on colorectal cancer. Critics say that the dose, 400 IU per day, was too small to make a difference.
More trials are needed to elucidate vitamin D’s benefits and risks at different doses and in different populations. In fact, a large-scale randomized trial that would include 20,000 U.S. women and men has been proposed by Harvard researchers and will be considered for funding by the National Institutes of Health. In the meantime, the evidence is so compelling that some experts already recommend at least 800 to 1,000 IU of vitamin D per day for adults