Many readers may have seen or heard news reports about a large study that (according to those news reports) implies that taking a daily multi-vitamin may reduce men’s overall, life-time risk for cancer.
The full text of this article by Gaziano et al. is available on line, and it is worth looking at in some detail.
The core objective of the study (the Physicians’ Health Study II) was to determine whether long-term use of multi-vitamin supplements could decrease risk for all cancers and for certain organ-specific cancers among a defined group of men of 50 or more years of age. It therefore tells us nothing about whether life-long use of multi-vitamin suplements may have such effects (although that is certainly possible).
The study was conducted as a randomized, double-blind, placebo-controlled trial, in which half the participants received a daily multi-vitamin tablet and the other half received a placebo. Here are the core data reported by Gaziano and his colleagues:
- The trial enrolled 14,641 male physicians between 1997 and 2001.
- All participants were aged at least 50 years at the time of enrollment.
- The average (mean) age of the participants at time of enrollment was 64.3 ± 9.2 years.
- 1,312/14,641 participants (9.0 percent) had a history of cancer at the time of enrollment.
- At a median follow-up of 11.2 years
- 2,669 participants had new, confirmed diagnoses of any cancer
- 1,373 participants had new, confirmed diagnoses of prostate cancer
- 210 participants had new, confirmed cases of colorectal cancer
- At the same median follow-up, compared to men taking the placebo, men treated with a daily multi-vitamin had
- A small, but statistically significant reduction in risk for diagnosis with any form of cancer (hazard ratio [HR] = 0.92; P = 0.04)
- No significant reduction in risk for diagnosis of prostate cancer (HR = 0.98; P = 0.76)
- No significant reduction in risk for diagnosis of colorectal cancer (HR = 0.89; P = 0.39)
- No significant reduction in risk for diagnosis of any other site-specific cancer
- No significant reduction in risk for cancer-specific mortality (HR = 0.88; P = 0.07)
- Also at the same median follow-up, among the 1,312 men with a prior history of cancer
- Daily multi-vitamin use was associated with a significant reduction in risk for new diagnosis of any cancer (HR = 0.73; P = 0.02)
- This degree of reduction in risk was similar to that seen among the 13,329 men who had had no prior history of cancer
- The study results also showed that the effect of multi-vitamin use was significantly affected by parental history of cancer.
- Men with no parental history of cancer had a beneficial effect of a daily multi-vitamin on total cancer (HR = 0.86; P = 0.02).
- Men with a parental history of cancer did not have any beneficial effect (HR = 1.05; P = 0.37).
Gaziano et al. conclude that the daily use of a multi-vitamin by male physicians of 50 years and older “modestly but significantly reduced the risk of total cancer.” The actual reduction was from 18.3 cancer events per 1,000 person-years for those taking the placebo to 17.0 cancer events per 1,000 person-years for those taking the multi-vitamin supplements (a 7.1 percent reduction in risk).
On the up-side, this study does seem to suggest that men with no parental history of cancer can reduce (slightly) their risk for cancer by use of a daily multi-vitamin regimen. On the down-side, however, this is yet another trial that shows no prostate cancer-specific preventive effect.