Low vitamin D and high homocysteine often go together, but treating both is unproven for heart attack or stroke - review
The Proposed Vitamin D–Homocysteine Relationship in Cardiometabolic Health: A Narrative Review of Mechanisms, Evidence, and Research Phenotypes
Nutrients (MDPI) 2026, 18, 3167, Sept 25, 2026, https://doi.org/10.3390/nu18193167
Yun-Ah Lee, Sung-Goo Kang
Summary by Claude Opus 5.5 - September 2026
Bottom line: Low vitamin D and high homocysteine often show up together. However, this 2026 review finds no proof yet that raising vitamin D reliably lowers homocysteine, or that treating both prevents heart attacks or strokes.
Study type: This is a peer-reviewed narrative review, not a meta-analysis, from the Catholic University of Korea. The authors screened 514 records and covered 23 studies in detail, plus landmark trials and Mendelian randomization (MR) studies. They did not pool results or score risk of bias.
Main findings
- Association: In 14,630 US adults (NHANES), each 10 ng/mL higher 25(OH)D went with 0.49 µmol/L lower homocysteine, but only at or below 21 ng/mL. Above that level there was no link. The MESA study (6,443 people) also found the link, but a Canadian survey (1,928 people) found none.
- Trials on homocysteine are mixed: In about 100 overweight women starting near 8.5 ng/mL, 50,000 IU of D3 weekly for 2 months cut homocysteine from 18.9 to 11.9 µmol/L, while placebo stayed at 17.9. The authors caution that "two frequently cited intervention publications report the same trial." In a separate trial, 2,000 IU/day for 12 weeks in 40 adults with epilepsy showed no difference. Achieved 25(OH)D levels were not reported.
- Mechanism: In animal and cell studies, vitamin D boosts enzymes that clear homocysteine. In the other direction, homocysteine increases CYP24A1, which breaks down active vitamin D. This suggests a possible two-way loop, but it has not been shown in humans.
- Hard outcomes: Large vitamin D trials (e.g., VITAL, 2,000 IU/day, 25,871 people) showed no clear cardiovascular benefit. In contrast, adding folic acid to blood-pressure medicine cut first stroke by 21% in hypertensive Chinese adults (CSPPT).
- The authors propose four vitamin D/homocysteine "phenotypes" for research use only.
What this does not show / limitations
- As a narrative review, it is selective and gives no pooled effect.
- The human data are mostly cross-sectional. Kidney function, B-vitamin status, obesity, age and season can all lower vitamin D and raise homocysteine at the same time.
- Many outcome trials enrolled people who were not deficient. The review says this "does not establish that deficient subgroups would benefit."
- No trial has tested vitamin D, with or without B vitamins, against heart attack or stroke in people with both low vitamin D and high homocysteine.
- AI tools assisted with drafting and screening, which the authors disclosed.
Related in VitaminDWiki
Stroke
- Stroke and Vitamin D meta-analyses - many studies
- Stroke risks increased if low Vitamin D: Death 3.6 X, recurrence 5.5 X – Meta-analysis
- After a TIA, the risk of ischemic stroke reduced 2.4X by a single loading dose of Vitamin D
- Strokes are both prevented and treated by Vitamin D
- Ischemic Stroke and Vitamin D - many studies
Heart Attack/Failure
- Severe rather than mild Heart Failure 3.4X more likely if low Vitamin D
- Heart Failure and Vitamin D meta-analyses - many studies
- Heart attack risk halved in adults with heart disease if >40 ng level of vitamin D (RCT)
- Those raising Vitamin D above 30 ng were 1.4 X less likely to die of Heart Attack (VA 19 years)
- Heart Failure 15X more likely if poor VDR, even if good level of vitamin D (China)