Published in the Journal of Clinical Oncology, the study reports that Chinese women who consume more soy before being diagnosed with lung cancer lived longer compared with those who consumed less soy.
The findings - which come from a large observational follow-up study conducted in Shanghai, China - provides the first scientific evidence that soy intake has a favourable effect on lung cancer survival by indicating the promising association between soy consumption and cancer survival.
"To our knowledge, this is the first study to suggest an association between high soy consumption before a lung cancer diagnosis and better overall survival," said lead study author Professor Gong Yang of Vanderbilt University Medical Center, USA.
"Although the findings are very promising, it's too early to give any dietary recommendations for the general public on the basis of this single study," he said.
A recent study by the same research team showed that high intake of soy food was associated with a 40% decrease in lung cancer risk.
The new study assessed the impact of soy intake on lung cancer survival among participants of the Shanghai Women's Health Study - which tracked cancer incidence in 74,941 Shanghai women.
Information on usual dietary intake of soy food (soy milk, tofu, fresh and dry soybeans, soy sprouts, and other soy products) was collected in-person at study enrolment and again two years later. Soy food and isoflavone content of various food products was calculated based on the Chinese Food Composition tables.
During the course of the study, 444 women were diagnosed with lung cancer, the team noted. In the main analysis, Yang and colleagues split these cancer patients into three groups according to soy food intake prior to lung cancer diagnosis.
Those with the highest soy food intake had markedly better overall survival compared with those with the lowest intake , said the authors - noting that 60% of patients in the highest intake group and 50% in the lowest intake group were alive at twelve months after diagnosis.
The team said that risk of death decreased with increasing soy intake until the intake reached a level equivalent to about 4 oz of tofu per day - with no additional survival benefit from consuming higher amounts of soy.
Similar trends were observed when dietary isoflavone intake was evaluated, said the authors.
"Given the increasing popularity of soy food in the U.S. and elsewhere, and a sizable number of women who don't smoke, the results of this study could have wider relevance," Yang sugegsted.
Source: Journal of Clinical Oncology
Published online ahead of print, doi: 10.1200/JCO.2012.43.0942
"Prediagnosis Soy Food Consumption and Lung Cancer Survival in Women"
Authors: Gong Yang, Xiao-Ou Shu, Hong-Lan Li, Wong-Ho Chow, et al