Daily supplements of vitamin C may lower levels of LDL (bad) cholesterol by five per cent, and subsequently reduce risk factors linked to cardiovascular disease, says a new meta-analysis.

Doses of at least 500 milligrams per day were necessary to produce these effects, which were accompanied by an 8.8 per cent reduction in triglyceride levels, according to the meta-analysis of 13 randomised, clinical trials published in the Journal of Chiropractic Medicine.

"Although the magnitude of change in LDL cholesterol and triglycerides appeared modest, it can be estimated […] that an LDL cholesterol change of -7.9 mg/dL could potentially translate to a 6.6 per cent reduction in coronary heart disease and that a change in triglycerides of −20.1 mg/dL could translate to a 2.4 per cent reduction in coronary heart disease risk," wrote Marc McRae from National University of Health Sciences in Lombard, Illinois.

Heart disease causes almost 50 per cent of deaths in Europe, and is reported to cost the EU economy an estimated €169 billion (£116 billion) per year.

On the other hand, no significant increases were observed in HDL cholesterol levels, stated McRae.

"This last result is surprising because numerous epidemiologic studies have shown that vitamin C intake positively correlates with HDL cholesterol concentrations," he added.

Pooled data

McRae identified 13 trials that included 14 separate groups including 405 subjects with high cholesterol levels (hypercholesterolemia). The subjects received vitamin C supplements of at least 500 mg per day for a period of three to 24 weeks. The studies were either a crossover double blind design or placebo-controlled double-blind design.

The average age of the study participants was 58.9, and 60 per cent of the subjects were men.

The pooled effect of the supplements on LDL blood levels was a reduction of 7.9 mg per dL, while HDL blood levels increased by 1.1 mg per dL. This latter result was not statistically significant, however, noted McRae.

"Supplementation with at least 500 mg/d of vitamin C, for a minimum of four weeks, can result in a significant decrease in serum LDL cholesterol and triglyceride concentrations. However, there was a non-significant elevation of serum HDL cholesterol," he said.

Mechanism

Commenting on the potential mechanism of action, McRae noted that vitamin C may intercept reactive oxygen species (ROS). This would have knock-on benefits for the inhibition of oxidative modification of LDL.

"This protection preserves the ability of LDL to be recognized by LDL receptors in the liver and therefore expedite its removal from the blood by LDL cholesterol catabolic pathways," he stated.

Another possible mechanism is a protective effect on LDL receptors. Animal studies have reported that the number of LDL receptors may decrease by as much as 25 per cent on consumption of a diet containing insufficient vitamin C

Limitations and take-home

McRae lists the potential limitations of his study, noting that the age range of the subjects was quite large, which could lead to confounding of the results.

"Average subject age varied between 48 and 82 years; and it is known hat vitamin C concentration in serum decreases with aging, whereas a concomitant increase in total serum concentration occurs," wrote Mc Rae. "Differences in age and dietary characteristics may result in unevenly matched baseline plasma vitamin C concentrations."

Other sources of error included the doses used, which ranged from 500 to 2,000 mg per day, and the duration of the study, which ranged from four to 24 weeks.

Despite the limitations, McRae concluded: "Although [the observed] changes are modest, any small change can have beneficial effects on the incidence of coronary heart disease, especially in light of the low cost and absence of toxicity when supplementing vitamin C within the ranges of 500 to 1000 mg/d."

Source: Journal of Chiropractic Medicine
June 2008, Volume 7, Issue 2, Pages 48-58
"Vitamin C supplementation lowers serum low-density lipoprotein cholesterol and triglycerides: a meta-analysis of 13 randomized controlled trials"
Author: M.P. McRae