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There’s a lot of research out there on supplements for cardiovascular disease (CVD) risk markers like LDL cholesterol (LDL-C) and blood pressure. All this research is for good reason: CVD is the cause of death[1] for around 50% of everyone in the world, and systolic blood pressure, LDL-C, and fasting plasma glucose levels are among the most predictive markers for dying from CVD. Presuming these relationships are causal (which is a pretty[2] good[3] assumption[4]), any intervention that reduces these markers can lower the risk of getting cardiovascular disease and ultimately dying from it.
But there’s an issue with having so much research on this important topic: it can be hard to navigate without losing sight of the big picture. That’s where umbrella reviews come in. Umbrella reviews are designed to summarize all the systematic reviews and meta-analyses on a given topic. One such umbrella review examining the effect of plant-based supplements on major cardiovascular risk markers was recently published[5]. The authors found 50 systematic reviews and meta-analyses looking at clinical trial evidence for a broad range of phytonutrient supplements. Since this is still quite a lot to process, this Mini narrows down their findings to the top five supplements by effect size for three major CVD risk markers in three separate tables below, along with some dosing information.
| Supplement | LDL-C reduction (mg/dL) | Effects on other blood lipids (mg/dL) | Usual dosage |
|---|---|---|---|
Red yeast rice | -33.64 (95% CI: -39.83 to -27.46) |
| 200–3,600 mg daily, with most studies dosing around 500–1,200 mg daily |
Fenugreek | -26.05 (95% CI: -50.39 to -1.70) | Total cholesterol: -25.12
| 10–60 grams of seed powder, or a variety of extracts whose specific dose depended on the extraction method used |
Spirulina | -19.02 (95% CI: -36.27 to -1.78) |
| 800 mg to 8 grams daily, with 2 grams being the most frequent daily dose |
Nigella sativa | -18.45 (95% CI: -22.44 to -14.45) |
| A wide range of oils, extracts, and powders were used. Roughly, extract doses were around 200–400 mg daily, powders and encapsulated solids were around 500– 2,000 mg daily, and oils were around 5 mL daily or 2,000–3,000 mg of encapsulated oil daily. |
Silymarin | -17.20 (95% CI: -28.50 to -5.91) |
| Usually 280–600 mg daily of extract |
| Supplement | Systolic blood pressure reduction (mmHg) | Effects on diastolic blood pressure (mmHg) | Usual dosage |
|---|---|---|---|
Sour tea (Hibiscus sabdariffa) | -7.58 (95% CI: -9.69 to -5.46) | -3.53 | Usually brewed tea using bags containing 1.25–3 grams sour tea 2–3 times daily, or 100 mg daily extract |
Ginger | −6.36 (95% CI: −11.27 to −1.46) | -2.12 | 0.5–3 grams ginger powder daily |
Garlic | −5.07 (95% CI: −7.30 to −2.85) | -2.48 | Supplements standardized to either 7.8–31.2 mg daily of alliin or 0.6–14.7 mg daily of S-allylcysteine |
Nigella sativa | −3.26 (95% CI: −5.10 to −1.42) | -2.80 | 0.5–1.6 grams of seed powder daily, or 0.2–3 grams of oil daily |
Pycnogenol | −3.22 (95% CI: −5.52 to −0.92) | -1.91 | 60–200 mg daily |
| Supplement | Fasting glucose reduction (mg/dL) | Effects on HbA1c (%) | Usual dosage |
|---|---|---|---|
Aloe vera | -30.05 (95% CI: -54.87 to -5.23) | n/a (studies that explored fasting glucose did not measure A1c) | Usually 1–2.8 grams of daily capsules, with 2 tablespoons juice and 0.2 grams of daily powder also used |
Blueberry or cranberry | -22.62 (95% CI: -37.72 to -7.52) | -0.54 | Blueberry: about 0.5–1 grams of hydroalcoholic extract or 1 gram of dried powder Cranberry: Either 240 mL of cranberry juice daily, 40 grams of dried cranberry, or 55 grams of raw cranberry |
Nettle (Urtica dioica) | -18.01 (95% CI: -30.04 to -5.97) | -0.77 | 1.5–10 grams daily |
Nigella sativa | 15.18 (95% CI: -19.82 to -10.55) | -0.45 | A wide range of oils, extracts, and powders were used. Roughly, extract doses were around 200–400 mg daily, powders and encapsulated solids were around 500–2,000 mg daily, and oils were around 5 mL daily or 2,000–3,000 mg of encapsulated oil daily |
Propolis (bee glue) | -13.51 (95% CI: -24.98 to -2.04) | -0.52 | 226.8–1,500 mg daily |
While the tables above are a decent starting point for evaluating the efficacy of these plant-based supplements, there are quite a few problems associated with direct comparisons.
The first is clear from the above table: some of the confidence intervals are very wide (e.g., Aloe vera for fasting glucose, ginger for blood pressure), indicating that the evidence is compatible with both large effects and close to no effect. Second, the heterogeneity of the evidence was very large for most of these values, indicating that studies with large differences in their populations, dosage forms, methodologies, and more were combined, raising the question of how meaningful these averages are. This problem is especially apparent in the meta-analysis that combined blueberry and cranberry supplements. Third, although the authors of this umbrella review rated the meta-analyses as mostly moderate or high quality, the evidence that went into them wasn’t always the best. Sometimes the studies were at high risk of bias, and some of the meta-analyses looked at studies that didn’t have control groups or good randomization. Thus, these values and rankings should be interpreted with caution. Finally, the populations were often quite different from one another. For example, some meta-analyses looking at blood glucose effects involved only people with type 2 diabetes, while others included broader populations.
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See other articles with similar topics: Cardiovascular Disease, Blood Pressure, LDL, Cholesterol, Systematic Review, Meta-analysis, Umbrella Review.
See other articles in Issue #80 (June 2021) of Study Deep Dives.
Other Articles in Issue #80 (June 2021)
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Deeper Dive: A Mendelian randomization study sheds light on the effects of polyunsaturated fatty acids on heart disease
This study explored whether genes that bump specific PUFA blood levels led to heart disease and found some evidence for the possible benefits of EPA.
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Deeper Dive: Can regular exercise and a good diet attenuate age-associated cognitive decline?
This large four-year trial found surprisingly little benefit from diet and exercise on brain health of older people. Here, we explore some possible reasons for this finding.
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Lower fat intake, lower testosterone levels?
This meta-analysis found that swapping out fat for carbs can lower men's testosterone levels a tad. But the relationship's neither set in stone nor straightforward.
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Interview: Elisabeth Bik, PhD
Microbiologist and scientific integrity consultant Elisabeth Bik discusses her background, the chilling effect of legal threats on scientific discourse, and more.
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CBD and pain: mechanism, mind, or both?
This study explored whether CBD's analgesic effect comes from its impact on people's biology or psychology.
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Meat in Mediterranean diets: helpful or hurtful for the heart?
How does adding increasing amounts of lean red meat to a Mediterranean diet affect lipids and lipoproteins? This study aimed to find out.
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Deeper Dive: Does red meat worsen glycemic control and inflammation?
This meta-analysis suggests that red meat doesn't impact glycemic control or inflammation in healthy adults, at least in the short term.
References
- ^ Ram Jagannathan, et al. Global Updates on Cardiovascular Disease Mortality Trends and Attribution of Traditional Risk Factors. Curr Diab Rep. (2019)
- ^ Eric Yuk Fai Wan, et al. Blood Pressure and Risk of Cardiovascular Disease in UK Biobank: A Mendelian Randomization Study. Hypertension. (2021)
- ^ Ference BA, et al. Low-density lipoproteins cause atherosclerotic cardiovascular disease. 1. Evidence from genetic, epidemiologic, and clinical studies. A consensus statement from the European Atherosclerosis Society Consensus Panel. Eur Heart J. (2017)
- ^ Stephanie Ross, et al. Mendelian randomization analysis supports the causal role of dysglycaemia and diabetes in the risk of coronary artery disease. Eur Heart J. (2015)
- ^ Tung Hoang, Jeongseon Kim. Phytonutrient supplements and metabolic biomarkers of cardiovascular disease: An umbrella review of meta-analyses of clinical trials. Phytother Res. (2021)
