Vitamin B and omega-3 fatty-acid supplementation over a period of five years failed to reduce the incidence of cancer and cancer mortality in patients with cardiovascular disease, research shows . The investigators did observe a statistically significant interaction by sex, however, with women taking omega-3 fatty acids at an increased for cancer and cancer mortality.
"People should be very careful when deciding to self-medicate with these dietary supplements because they are active substances," lead investigator Dr Valentina Andreeva (University of Paris, France) told heartwire . "The findings need to be confirmed and should be interpreted with caution, but there is some indication that they might have adverse effects. Taking these supplements without a physician's advice and over the long term might not be a good idea."
The researchers caution against reading too much into the increased cancer risk in women taking the omega-3 fatty acids, given that there were only 29 cancer cases in females, compared with the 145 cases that occurred in males, so the findings are preliminary and hypothesis-generating for future studies.
The SU.FOL.OM3 Study
Known as the Supplementation with Folate, Vitamins B6 and B12 and/or Omega-3 Fatty Acids (SU.FOL.OM3) trial and published online February 13, 2012 in the Archives of Internal Medicine, the study was designed as a secondary cardiovascular disease prevention study. The main results showed that treatment with vitamin B or omega-3 fatty acids had no effect of major vascular events. Given the availability of the data, the researchers examined the benefit of these supplements on cancer risk, because there is inconsistency across trials, with some studies suggesting a protective effect with omega-3 fatty acids and vitamin B and some studies showing a lack of benefit.
In SU.FOL.OM3, 2501 individuals aged 45 to 80 years old were randomized in a 2x2 factorial design to one of four study arms: 5-methlytetrahyrdofolate 0.56 mg, 3-mg vitamin B6, and 0.02-mg vitamin B12; eicosapentaenoic and docosahexaenoic acid 600 mg; B vitamins and omega-3 fatty acids; or placebo.
After five years of treatment with the supplements, new incident cancer was confirmed in 7.0% of patients, and death from cancer occurred in 2.3% of the study population. There were 47 deaths in men (2.4%) and 11 deaths in women (2.1%). In an age- and sex-adjusted multivariable model, there was no effect of the B vitamins on cancer incidence and cancer mortality, a lack of effect on cancer incidence and mortality in patients treated with omega-3 fatty acids, and a lack of effect in patients who received omega-3 fatty acids and B-vitamin supplementation.
The results confirm the findings of the Study of the Effectiveness of Additional Reductions in Cholesterol and Homocysteine (SEARCH), a study reported by heartwire that showed the addition of folic acid and vitamin B did not have any effect on vascular events compared with placebo in a trial in more than 12 000 MI survivors.
There was a positive association observed in women who were treated with omega-3 fatty acids, with these women having a threefold greater risk of developing cancer (hazard ratio [HR] 3.02; 95% CI 1.33–6.89) and a fivefold increased risk of dying from cancer (HR 5.49; 95% CI 1.18–25.97). However, as the researchers point out, there were just 21 cases of cancer in the patients who received omega-3 fatty acids and eight cases among those assigned to the control group, resulting in very wide confidence intervals.
Andreeva said the five-year follow-up in SU.FOL.OM3 is short, but investigators hypothesized that if there were any adverse effects with the two supplements, the risk might be the promotion of preexisting clinical lesions. "We did not really expect it to show an effect on cancer initiation, given the decades it takes for cancer to develop," she said.