DENVER — Elevated plasma homocysteine wasn't linked to an overall increase in cancer incidence or mortality in the Women's Health Study.
Indeed, of the 13 most common site-specific forms of cancer in the prospective study, only lung cancer—the fourth most common—was associated with an elevated homocysteine level, Dr. Yiqing Song reported at the annual meeting of the American Association for Cancer Research.
Of 27,764 participants in the Women's Health Study who were at least 45 years old and apparently healthy when they gave a baseline blood sample, 2,637 went on to develop cancers other than nonmelanoma skin cancer during a median follow-up of 13 years. There were 511 deaths due to malignancy.
The adjusted risk of lung cancer was 83% greater among those with a plasma homocysteine level in the highest quintile, with a median level of 15.9 micromol/L, compared with those with levels in the lowest quintile, with a median of 7.44 micromol/L. There were 199 cases of lung cancer during the study period.
But no other type of cancer was significantly related to plasma homocysteine level. Of the other 12 most common cancers, 9 were less common in women with elevated homocysteine levels, but none of the inverse associations achieved statistical significance.
For example, the risk of breast cancer—by far the most common malignancy in the Women's Health Study, with 1,099 cases—was an adjusted 6% less among women with a homocysteine level in the top quintile, compared with those whose level was in the lowest quintile.
The study hypothesis was that an elevated plasma homocysteine level would predict increased cancer risk. A high level of homocysteine is typically caused by inadequate intake of folate and other B vitamins. Deficiencies of these vitamins are believed to promote carcinogenesis through disruption of DNA methylation, repair, and synthesis, explained Dr. Song of Brigham and Women's Hospital, Boston.
In the Women's Health Study, an elevated homocysteine level was associated with a many potentially confounding variables. For instance, women with higher plasma homocysteine were significantly less physically active, heavier, more likely to smoke, and had greater alcohol intake than those with a low homocysteine level. They were also less likely to be on postmenopausal hormone therapy or to take a multivitamin, and they ate fewer fruits and vegetables and more red meat. Multivariate risk adjustment was therefore essential.