BackgroundHigh level of serum cholesterol is considered to be a major risk factor for cardiovascular disease (CVD). A double-blinded, randomized, placebo-controlled trial was performed to test the hypothesis that a daily intake of Chlorella may improve serum lipid profile through enhancement of serum carotenoid concentration in mildly hypercholesterolemic subjects.MethodsEligible subjects (n = 63) were randomized to either Chlorella (5 g/day) or placebo for a double-blinded trial with a 2-week lead-in period and a 4-week intervention period. Serum triglycerides, total cholesterol, lipoproteins, apolipoproteins and carotenoids were assessed at the beginning and the end of the trial.ResultsCompared with the control group, the Chlorella group exhibited remarkable changes in total cholesterol (Chlorella −1.6%; placebo 0.03%; P = 0.036), triglycerides (Chlorella −10.3%; placebo 11.9%; P = 0.002), lutein/zeaxanthin (Chlorella 89.6%; placebo −1.7%; P < 0.0001), and α-carotene (Chlorella 163.6%; placebo 15%; P < 0.0001). Improvement of serum lipids was supported by significant reductions of very low-density lipoprotein cholesterol (Chlorella −11%; placebo 11.8%; P = 0.006), apolipoprotein B (Chlorella −1.5%; placebo 1.7%; P = 0.044), non high-density lipoprotein (Chlorella −2.6%; placebo −0.5%; P = 0.032), and high-density lipoprotein/triglycerides (Chlorella 4.0%; placebo −9.5%; P = 0.023), suggesting an inhibitory effect of Chlorella on the intestinal absorption of dietary and endogenous lipids. Further, the changes of serum lipids appeared to be associated with the changes of serum carotenoids.ConclusionDaily consumption of Chlorella supplements provided the potential of health benefits reducing serum lipid risk factors, mainly triglycerides and total cholesterol, in mildly hypercholesterolemic subjects. The effect was related to carotenoid consumption.Trial registrationWHO International Clinical Trials Registry Platform KCT0000259.