The study "Association between Blood Vitamin D and Myocardial Infarction: A Meta-analysis Including Observational Studies" explores the relationship between vitamin D levels and the risk of myocardial infarction (MI). By analyzing data from eight observational studies, the researchers aim to determine whether sufficient levels of blood vitamin D offer protective effects against MI.
Methodology
Data Sources and Selection
- The meta-analysis followed the Meta-Analysis of Observational Studies in Epidemiology (MOOSE) guidelines.
- Databases searched: PubMed, EMBASE, and Web of Science (up to February 2017).
- Inclusion criteria:
- Observational studies with MI cases and controls.
- Reported blood 25-hydroxyvitamin D (25[OH]D) levels or vitamin D sufficiency rates.
- Quality assessment:
- Studies were evaluated using the Newcastle-Ottawa Scale (NOS). Five studies scored >7, indicating high quality.
Statistical Analysis
- Statistical methods included WMD for vitamin D levels and OR for MI risk.
Heterogeneity:
- Significant heterogeneity was observed (I² = 95.3%, p < 0.001 for vitamin D levels).
- Sensitivity analysis confirmed robust results.
Publication bias:
- No significant bias detected (Begg’s test, p = 0.707; Egger’s test, p = 0.088).
Key Findings
Blood Vitamin D Levels in MI Patients vs. Controls
- The meta-analysis included 9913 participants (3411 MI cases and 6502 controls).
- MI patients had significantly lower blood vitamin D levels compared to non-MI controls:
- Weighted Mean Difference (WMD): −3.40 ng/mL (95% Confidence Interval [CI]: −5.87 to −0.92, p = 0.007).
- Subgroup analyses showed geographic variations:
- Asia: MI patients had substantially lower vitamin D levels (WMD = −8.78 ng/mL, 95% CI: −11.96 to −5.61, p < 0.001).
- America: WMD = −1.50 ng/mL (95% CI: −2.38 to −0.62, p = 0.001).
- No significant associations were observed in Europe and Oceania.
Vitamin D Sufficiency and MI Risk
- Sufficient vitamin D levels appeared to protect against MI:
- Odds Ratio (OR): 0.44 (95% CI: 0.25 to 0.76, p = 0.004).
- Subgroup results:
- Protective effects were observed in Asia (OR = 0.20, 95% CI: 0.10 to 0.43, p < 0.001) and America (OR = 0.61, 95% CI: 0.45 to 0.82, p = 0.001).
- No significant association was found in Europe.
Discussion
Vitamin D Deficiency and MI
- Low vitamin D levels may contribute to MI risk through several mechanisms:
- Activation of the renin-angiotensin-aldosterone system (RAAS), leading to hypertension.
- Association with atherosclerosis via elevated parathyroid hormone (PTH).
- Regulation of inflammatory cytokines, reducing inflammation linked to cardiovascular events.
Geographic Differences
- The significant association in Asia may reflect higher rates of vitamin D deficiency due to cultural and environmental factors, such as limited sun exposure.
Implications for Treatment
- While the findings suggest vitamin D sufficiency could reduce MI risk, results for vitamin D supplementation remain mixed:
- Some studies suggest no impact on cardiovascular outcomes.
- Others propose that moderate to high-dose supplementation could lower cardiovascular risk.
Limitations
- The meta-analysis included only observational studies, which limits causal inferences.
- Significant heterogeneity across studies may affect result reliability.
- Lack of subgroup analysis for factors like age, sex, and seasonal variation of vitamin D levels.
Conclusion
This meta-analysis concludes that MI patients have significantly lower blood vitamin D levels compared to controls, particularly in Asia and America. Sufficient vitamin D levels may offer protective effects against MI. Further large-scale, multicenter clinical trials are needed to explore causality and the potential benefits of vitamin D supplementation in preventing MI.
For full details, refer to the original article: https://pubmed.ncbi.nlm.nih.gov/28645551/
