One of the roles I play is interpreter. It's still a bit of surprise to me how much of a disconnect there is between the doctor and the patient but they really are speaking different languages. Not all of that is the physician's fault. I do think there needs to be a manual entitled, "How to be a good patient". But right now, I'm the go between. One of my brother's questions was whether he should take a multi-vitamin. The oncologist suggested it might be a good idea and I disagreed. Neither one of us seemed to have a terribly strong opinion either way so I thought I'd go back and review the literature regarding vitamin use.
So is there a role for multi-vitamins in general? In certain instances, there appears to be. Pregnancy comes to mind. Since the implementation of prenatal vitamins, neural tube defects have decreased. Interestingly, a meta analysis concluded that there was a trend towards a decrease in pediatric cancers in those situations where the mom took a prenatal while pregnant. Certainly in cases where malnutrition exists multivitamins can help. But when I look at the data from large populations where food is plentiful, there doesn't seem to be much evidence that the ingestion of a multivitamin helps to prevent cancer. Some studies find an actual increase such as this study that showed a very mild increase in breast cancer in Swedish women. Or, the often referenced ATBC study where heavy smokers randomized to beta-carotene had a 20% higher chance of developing lung cancer. Likewise, the CARET study found that in smokers or asbestos exposed workers, those taking beta-carotene and vitamin A had increased lung cancer rates. The Physicians Health Study took ~11,000 physicians and gave them beta-carotene while another ~11,000 of them received a placebo. Approximately 10% were current smokers and ~40% were former smokers. No effect on either cancer rates or cardiovascular disease were seen. The Woman's Health Initiative looked at ~90,000 women in an observational study and nearly 70,000 women in interventional studies. It did not find any effect of vitamin intake on cancer, heart disease or mortality. Most of the data showing benefit are in smaller populations or in malnourished people. All in all, the data seem sketchy at best with respect to cancer prevention. There doesn't seem to be a clear benefit and in some cases liker smokers or asbestos exposed people, they may make it worse.
All of those trials were prevention. But what about as an adjunct to therapy? One argument for it is that chemo is incredibly rough on the body for a hole host of reasons. On top of that, the patient is often not eating so it's not a stretch to conceive that the patient is becoming malnourished. But there just aren't any good data to say that supplements are the way to go for someone who is able to eat. The American Cancer Society recommends that patients get their nutrition from food but a multivitamin "is a good choice for anyone who, for whatever reasons, cannot eat a healthful diet." They also outline where in certain cases, supplements are warranted based on blood levels of vitamin D, B12, etc. No argument there. If there is diagnosed and a quantifiable deficiency, then it is reasonable to supplement it back. The National Cancer Institute concludes "there is no scientific evidence that dietary supplements or herbal remedies can cure cancer or stop it from coming back. The NCI strongly urges you to depend on traditional, healthy foods for vitamins, minerals, and other nutrients." The oncologist referred to one interventional study but I haven't yet been able to find it. I think it was in the context of B12 deficiency. I'll have to get the specific trial next time we're in the office to give the matter a thorough consideration.