A report published in the May 2006 issue of the American Journal of Clinical Nutrition revealed that consuming soy isoflavones for four months resulted in higher B cell counts and a reduction in DNA damage in a group of postmenopausal women.

Fifty-two women between the ages of 50 and 65 were assigned to receive cow's milk plus a placebo supplement, soymilk (providing 71.6 mg isoflavones) plus a placebo supplement, or cow's milk plus a 70 milligram isoflavone supplement daily for sixteen weeks. Blood and urine samples were analyzed at the beginning and conclusion of the study for lymphocyte (white blood cell) subsets, cytokines, and inflammation and oxidative damage markers.

At the end of the study, plasma concentrations of the isoflavone genistein were significantly higher in women who received soymilk or isoflavone supplements than than in those who received the cow's milk/placebo combination. Although women who received isoflavones did not experience an increase in such factors as gamma interferon or interleukin 2, white blood cells known as B lymphocytes were higher among women who received either form of soy than in those who did not receive soy, with subjects who received the isoflavone supplement experiencing the greatest increase. Plasma 8-hydroxy-2-deoxy-guanosine, a marker of oxidative DNA damage, was lower in women who received the two soy-containing regimens than among those who received no soy.

The authors discuss the fact that isoflavones have nonhormonal properties that can benefit older individuals, particularly their ability to function as antioxidants and protect against diseases that result from oxidative damage. They note that the increase in B cells in response to the estrogenic action of isoflavones is in agreement with earlier studies that have shown that estrogen enhanced humoral immunity. They recommend research to determine the effect of soy isoflavones in immunologically challenged individuals.