Vitamin D supplementation significantly improved several cardiometabolic risk factors, with effects varying based on demographic and clinical characteristics. 

In a meta-analysis, published in Engineering, investigators examined 99 randomized controlled trials (RCTs) involving 17,656 participants aged 6 to 75 years (median age: 50.35 years) from both Western (n = 48) and non-Western (n = 51) countries up to March 26, 2024. They focused on the effects of vitamin D supplementation on blood pressure, blood lipids, and glycemic parameters. 

The investigators conducted a systematic search of PubMed, Web of Science, and Embase databases for RCTs published up to March 26, 2024. Eligible studies included those written in English, conducted in humans, with a comparable placebo or control group, and reporting relevant outcomes for blood pressure, lipid profile, and glycemic parameters.

Data extraction included author information, publication year, study location, study design, number of participants, health status, age, intervention details, and outcome measures. The risk of bias was evaluated using the Cochrane Collaboration Handbook recommendation, and the quality of evidence was assessed using the GRADE approach.

Statistical analysis employed a random-effects model to generate effect sizes for cardiometabolic risk factors, expressed as weighted mean differences and 95% confidence intervals (CI). Heterogeneity was assessed using I² statistics, with subgroup analyses performed based on ethnocultural background, baseline 25[OH]D levels, body mass index (BMI), vitamin D dosage, age group, and intervention duration.

Vitamin D supplementation had overall beneficial effects on blood pressure, blood lipids, and glycemic parameters, with more pronounced benefits observed in specific subgroups.

Among the key findings were:

• Blood Pressure: Vitamin D supplementation significantly reduced both systolic blood pressure (SBP) (–2.04 mmHg, 95% CI = –3.50 to –0.59) and diastolic blood pressure (DBP) (–3.00 mmHg, 95% CI = –3.61 to –2.39).
• Blood Lipids: Total cholesterol (TC) levels decreased significantly (–0.12 mmol/L, 95% CI = –0.21 to –0.03), whereas no significant effects were observed for low-density lipoprotein (LDL)-C, high-density lipoprotein (HDL)-C, and triglycerides in the overall population.
• Glycemic Parameters: Significant reductions were observed in fasting blood glucose (FBG) (–0.13 mmol/L, 95% CI = –0.20 to –0.05), hemoglobin A1C (A1C) (–0.09%, 95% CI = –0.13 to –0.05), and fasting blood insulin (FBI) (–7.61 pmol/L, 95% CI = –11.93 to –3.30).

Subgroup analyses revealed several important effect modifiers:

• Ethnocultural Background: Non-Western populations showed more pronounced benefits in glycemic parameters compared with Western populations.
• Baseline 25-hydroxyvitamin D (25[OH]D) Levels: Participants with baseline 25[OH]D levels < 15.0 ng/mL experienced greater improvements in blood pressure and glycemic parameters.
• BMI: Participants with BMI < 30 kg/m² demonstrated more significant improvements in SBP and glycemic parameters compared with those with BMI ≥ 30 kg/m².
• Age: Participants aged ≥ 50 years showed greater benefits in most outcomes compared with younger participants.
• Vitamin D Dosage: Higher doses (≥ 3,320 IU/day) were associated with more significant improvements in SBP, LDL-C, and A1C compared with lower doses.
• Intervention Duration: Longer intervention periods (≥ 3 months) resulted in greater improvements in LDL-C, TC, and FBG levels compared with shorter durations.

The baseline range of 25[OH]D in the included participants was 5.59 to 35.01 ng/mL (median value = 15.00 ng/mL). Forty-five studies reported baseline values < 15.0 ng/mL, and 44 studies reported values ≥ 15.0 ng/mL.

The BMI of participants ranged from 2.72 to 37.9 kg/m² (median value: 30.0 kg/m²). Fifty-one studies reported median BMI < 30.0 kg/m², and 32 studies reported BMI ≥ 30 kg/m².

Vitamin D doses in the included studies ranged from 40 to 120,000 IU/day (median dose = 3,320 IU/day). Forty-seven studies used doses < 3,320 IU/day, and 48 studies used doses ≥ 3,320 IU/day.

Intervention duration ranged from 6 weeks to 7 years.

Significant reductions in SBP and DBP were observed in both Western and non-Western populations, across age groups, and intervention durations. However, significant effects were only observed in participants with baseline 25[OH]D < 15.0 ng/mL, BMI < 30 kg/m², and vitamin D supplementation dose ≥ 3,320 IU/day.

LDL-C levels significantly decreased in participants with high baseline 25[OH]D levels (≥ 15.0 ng/mL), high vitamin D dosage (≥ 3,320 IU), long intervention duration (≥ 3 months), and all age groups. TC levels improved in non-Westerners but not in Westerners, as well as in individuals with lower baseline 25[OH]D levels (< 15.0 ng/mL), longer intervention duration (≥ 3 months), and older age groups (≥ 50 years).

Vitamin D supplementation improved all glycemic parameters in non-Westerner individuals, whereas no effect was observed in Westerner individuals. Significant improvements were seen in participants with lower baseline 25[OH]D levels, lower BMI, higher vitamin D dosage, older age, and longer intervention duration.

Meta-regression analysis indicated significant differences in the supplemental effect of vitamin D on TC levels between subgroups stratified by baseline 25[OH]D levels (P = .039) and on FBI between subgroups stratified by baseline 25[OH]D levels (P = .005) and BMI (P = .045).

The study had several limitations, including the lack of evidence regarding improvement in cardiovascular outcome events and incidence of type 2 diabetes, insufficient intervention periods in some RCTs, and high heterogeneity in most results.

The authors declared having no competing interests.