I previously thought only certain fat-soluble vitamins like E, A and beta-carotene were harmful when taken in extra amounts — Google my name for details in past columns. But remember that article I wrote Nov. 5 about studies showing that taking extra folic acid, a water-soluble vitamin, increased prostate cancers in men and pre-cancerous polyps of the colon in men and women? Well, it gets worse.

A study in the Nov. 18, 2009, issue of the Journal of the American Medical Association that for some reason flew largely under the radar gave folks with a common and often silent condition — diseased heart vessels (coronary artery disease) — 0.8 milligrams of daily folic acid and 0.4 milligrams of vitamin B12. Those taking these had a 38 percent higher chance of dying from cancer, especially lung cancer, and indeed had an increased risk of dying from any cause.

According to the authors, extra folic acid may stimulate the growth of both cancers and pre-cancers. It may also reduce the ability of our body's own natural killer cells to destroy pre-cancers, impairing immunity. So there's little reason to think that increased cancers would be limited to folks with heart disease. The study was high quality in that it was randomized, involved thousands of subjects, and lasted several years with minimal loss of participants to follow-up. The average age of folks in the study was 62, and most were men, so younger women should continue to take at least 0.4 milligrams of folic acid daily during and even before pregnancy to prevent birth defects.

A smaller study in the January 2009 issue of Asian Cardiovascular & Thoracic Annals also looked at folks with diseased heart vessels, namely, those who had had unstable angina or so-called non-ST-elevation myocardial infarction (a type of heart attack) in the previous two weeks. It found that those who took a combination of folic acid and vitamins B12 and B6 over the following six months had more deaths, angina and hospitalizations.

CNN-Health recently interviewed Dr. Donald Abrams, chief of hematology and oncology at San Francisco General Hospital, about what to take after getting breast cancer. Not only did he say that nutrients are much better obtained from foods rather than vitamin and mineral supplements, but he specifically recommended against taking a multivitamin, which he felt could lead to excess intake of some vitamins that may actually be harmful.

Abrams did note a growing body of evidence linking vitamin D deficiency with breast cancer, and suggested taking 1,000 IU to 2,000 IU a day of vitamin D.

Dr. Landis Lum is a family practice physician for Kaiser Permanente and an associate clinical professor at the University of Hawai'i John A. Burns School of Medicine. Send questions to islandlife@honoluluadvertiser.com with "Prescriptions" in the subject line, or mail to Prescriptions, Island Life, The Honolulu Advertiser, 605 Kapi'olani Blvd., Honolulu, HI 96813. This column is not intended to provide medical advice.