Further bad news about antioxidants
Antioxidant supplements appear to reduce the effectiveness
of lipid lowering drugs, according to American researchers. The findings
follow several trials that have failed to show the value of antioxidant
therapy in preventing or treating cardiovascular disease.
Dr Marian Cheung and colleagues from the school
of medicine, University of Washington, conducted a 12-month trial involving
153 patients. Participants were divided into four treatment groups to
receive simvastatin and niacin; antioxidant supplements only; simvastatin,
niacin and antioxidants; or placebo. The antioxidant supplements used
were b-carotene 12.5mg, vitamin C 500mg, vitamin E 400IU and selenium
50µg, all given twice a day.
After 12 months, only minor changes in lipid levels
were seen in the placebo and antioxidant-only groups. Significant decreases
in plasma cholesterol, triglycerides, low-density lipoprotein (LDL) cholesterol
and very low-density lipoprotein (VLDL) cholesterol were seen in all patients
receiving simvastatin and niacin, regardless of whether they were also
receiving antioxidants.
However, in patients taking antioxidants, the favourable
increases in high-
density lipoprotein (HDL) cholesterol caused by simvastatin and niacin
were reduced. The changes in HDL levels seen in the group receiving antioxidants,
simvastatin and niacin did not differ significantly from those seen in
the placebo group. This blunting of response was uniform between smokers
and non-smokers, and people with or without diabetes or hypertension.
The researchers comment: “The design of the study
precludes us from determining which one or more of the components of the
antioxidant cocktail was responsible for this effect.” The researchers
say that the increase in HDL seen in the simvastatin-niacin group is likely
to be an effect of niacin because simvastatin only has a modest effect
on HDL at the low dose used in the study. Therefore, they speculate that
the blunting of HDL response is likely to be as a result of the antioxidants’
effect on niacin (Atherosclerosis, Thrombosis and Vascular Biology
2001;21:1320).
In an accompanying leading article, Dr Lewis Kuller,
an epidemiologist at the University of Pittsburgh, comments: “Given the
lack of efficacy of antioxidants in clinical trials to date, antioxidant
vitamin combinations above the recommended dietary allowances should not
be recommended for prevention or treatment of cardiovascular disease.
It will be important for physicians to advise their patients that use
of antioxidants could be hazardous, especially in combination with lipid-lowering
drugs.” (ibid, p1253.)
Back to Top
|
