While previous research has suggested a link between low levels of vitamin D in the blood and an increased risk of cardiovascular disease, a new Michigan State University study has found that taking vitamin D supplements did not reduce that risk. The large-scale study found that vitamin D supplements did not decrease the incidence of heart attacks, strokes or other major adverse cardiovascular events.
"We thought it would show some benefit," said Dr Mahmoud Barbarawi, a clinical instructor in the MSU College of Human Medicine and chief resident physician at Hurley Medical Centre in Flint, Michigan. "It didn't show even a small benefit. This was surprising."
His finding was consistent for both men and women and for patients of different ages. Many earlier studies have found an association of low levels of vitamin D in the blood and an increased risk of cardiovascular disease, suggesting that vitamin D supplements might reduce that risk.
Barbarawi led a team of researchers and reviewed data from 21 clinical trials, including more than 83,000 patients. Half the patients were administered vitamin D supplements, and half were given placebos. The meta-analysis of data showed no difference in the incidence of cardiovascular events or all causes of death between the two groups.
Vitamin D sometimes is known as the sunshine vitamin, because human skin makes vitamin D when exposed to the sun. Thus, those living farthest from the equator tend to have lower levels of vitamin D in their blood.
While some studies have found a link between low levels of the vitamin and an increased risk of adverse cardiovascular events, Barbarawi's study suggests that other factors, such as outdoor physical activity and nutritional status, might explain the association.
Barbarawi also noted that even though his findings showed no effect on heart health, some patients, such as those being treated for osteoporosis, still might benefit from the supplements.
As a result, he suggests that doctors and patients think twice about taking the vitamin to minimise the chances of a heart attack or other cardiovascular issues. "We don't recommend taking vitamin D to reduce this risk," Barbarawi said.
Importance: Observational studies have reported an association between low serum vitamin D levels and elevated risk of cardiovascular disease (CVD) events, but such studies cannot prove causation because of possible unmeasured confounding.
Objective: We conducted a meta-analysis of randomized clinical trials that tested the association of vitamin D supplementation with reduced CVD events and all-cause mortality.
Data Sources: Literature search through PubMed, the Cochrane Library, and Embase was completed by 2 reviewers from each database’s inception to December 15, 2018.
Study Selection: Inclusion criteria were randomized clinical trials that reported the effect of long-term (≥1 year) vitamin D supplementation on CVD events and all-cause mortality. Studies that did not include cardiovascular outcomes were excluded.
Data Extraction and Synthesis: Data were abstracted independently by 2 authors. Random-effects models were used to report the risk ratios (RRs) and 95% CIs.
Main Outcomes and Measures: Major adverse cardiovascular events was the primary outcome, and rates of myocardial infarction, stroke or cerebrovascular accident, CVD mortality, and all-cause mortality were the secondary end points.
Results: Twenty-one randomized clinical trials were included (including 83 291 patients, of whom 41 669 received vitamin D and 41 622 received placebos). The mean (SD) age of trial participants was 65.8 (8.4) years; 61 943 (74.4%) were female. Only 4 trials had prespecified CVD as a primary end point. Vitamin D supplementation compared with placebo was not associated with reduced major adverse cardiovascular events (RR, 1.00 [95% CI, 0.95-1.06]; P = .85) nor the secondary end points of myocardial infarction (RR, 1.00 [95% CI, 0.93-1.08]; P = .92), stroke (RR, 1.06 [95% CI, 0.98-1.15]; P = .16), CVD mortality (RR, 0.98 [95% CI, 0.90-1.07]; P = .68), or all-cause mortality (RR, 0.97 [95% CI, 0.93-1.02]; P = .23). Results were generally consistent by sex, baseline 25-hydroxyvitamin D level, vitamin D dosage, formulation (daily vs bolus dosing), and presence or absence of concurrent calcium administration.
Conclusions and Relevance: In this updated meta-analysis, vitamin D supplementation was not associated with reduced major adverse cardiovascular events, individual CVD end points (myocardial infarction, stroke, CVD mortality), or all-cause mortality. The findings suggest that vitamin D supplementation does not confer cardiovascular protection and is not indicated for this purpose.
Mahmoud Barbarawi, Babikir Kheiri, Yazan Zayed, Owais Barbarawi, Harsukh Dhillon, Bakr Swaid, Anitha Yelangi, Saira Sundus, Ghassan Bachuwa, Mohammad Luay Alkotob, JoAnn E Manson