Meta-analysis Shows Turmeric Effective in Lowering Low-density Lipoproteins and Triglycerides
Cardiovascular disease (CVD) is one of the leading causes of mortality in the world, and the increased risk is characterized by age, sex, hypertension, dyslipidemia, obesity, type 2 diabetes mellitus, and metabolic syndrome (MetS). Treatment of dyslipidemia is important for the prevention of CVD. Statins have shown promise in the treatment of dyslipidemia, but they have a potential for serious adverse effects, including hepatotoxicity. Therefore, there is a need for safe and effective alternatives. Turmeric (Curcuma longa, Zingiberaceae) rhizome and curcumin, an active constituent of turmeric, have been found to be effective in treating many of the risk factors for CVD, including dyslipidemia. However, there have been conflicting studies, and a previous meta-analysis failed to demonstrate a significant lipid-lowering effect of curcumin.1 This previous meta-analysis had many limitations, according to the authors. The goal of the present meta-analysis was to address these limitations and to assess the efficacy and safety of turmeric and curcumin in lowering lipid levels in patients with risk factors for CVD.
Online databases PubMed, Embase, Ovid, Medline, and Cochrane Library were searched for clinical studies published in English as of November 2016. Search terms included curcuminoid or curcumin or Curcuma or turmeric or curcuminoids and hyperlipidemia or hyperlipidemic or hypolipidemic or dyslipidemia or dyslipidemia or hypercholesterolemia or hypercholesterolemic or hypocholesterolemic or low-density lipoprotein or high-density lipoprotein or cholesterol or triglycerides or hypertriglyceridemia or hypotriglyceridemic. Inclusion criteria included drug/placebo-controlled parallel randomized trials; subjects with risk factors for CVD; use of purified curcumin or a curcuminoid mixture, standardized extracts with noted content of curcumin, or turmeric powder, regardless of dosage and frequency; a study duration ≥ 4 weeks; and reported mean ± standard deviation, mean ± standard error, or median (range) of between-group differences at the beginning and end of the trial. Studies were excluded if they were a crossover randomized design, included non-comparative data, had a duration of treatment less than four weeks, or lacked outcome measures. Outcome measures included serum levels of low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides (TG), and total cholesterol (TC). A secondary outcome was any adverse effects due to curcumin or turmeric products.
In 1566 relevant articles, seven randomized controlled trials with a total of 649 patients met all inclusion criteria and were selected for analysis. All studies were double-blind, except for two, and had a duration from four weeks to six months. The studies took place in Iran (n = 2), India (n = 2), Thailand, Taiwan, and Pakistan. Six of the seven studies used placebo as control; one used metformin in both treatment (amount unspecified) and control (1 g/day). Pooled data from six studies (n = 218 both cases and controls) showed that all herb forms significantly reduced serum LDL-C (P < 0.0001). Meta-analysis of data from seven studies showed a benefit of experimental treatment (n = 325) compared to controls (n = 324) in significantly reducing TG (P = 0.007).
To assess potential bias, subgroup analysis was done in patients with MetS and hyperglycemia. There was a significant effect on serum TC levels in two studies including patients with MetS (P < 0.0001), with respect to serum TC levels between the experimental (n = 67) and placebo (n = 69) groups. Pooled data from four studies showed no significant difference between placebo (n = 149) and treatment (n = 151) groups for those with hyperglycemia (P = 0.612). “Serum HDL-C levels were not obviously improved.” Turmeric and curcumin appear to be well tolerated with no serious adverse events reported in any of the studies, though minor adverse reactions were reported ranging from dyspepsia to hot flashes.
The authors conclude that turmeric and curcumin have a cardioprotective effect, lowering serum LDL-C and TG levels. While turmeric and curcumin also lowered serum TC levels in patients with MetS, they did not show the same effect in other groups, leaving the efficacy for TC levels inconclusive. Admitted limitations include interpretability of outcomes, lack of unpublished studies or studies published in the grey literature, lack of diversity in study patients (all were Asian), and that some data were obtained indirectly, which may affect the results of the subgroup analysis. The authors state, “Due to uncertainties related to dosage form, dose and medication frequency, it is premature to recommend the use of turmeric or curcumin in clinical settings.”
The study was funded by the Natural Science Foundation of China, the “Par-Eu Scholars Program” of Chongqing City, and the National Science and Technology Major Project of China.
1Sahebkar A. A systematic review and meta-analysis of randomized controlled trials investigating the effects of curcumin on blood lipid levels. Clin Nutr. 2014;33(3):406-414.
Qin S, Huang L, Gong J, et al. Efficacy and safety of turmeric and curcumin in lowering blood lipid levels in patients with cardiovascular risk factors: a meta-analysis of randomized controlled trials. Nutr J. 2017;16(1):68. doi: 10.1186/s12937-017-0293-y.