Use of cod liver oil supplements was associated with a 44 per cent lower risk of death for lung cancer patients, while daily use of other dietary supplements was associated with a 30 per cent reduction in the risk of death among lung cancer patients, according to findings published in the International Journal of Cancer.
“This study has shown that in lung cancer patients taking dietary supplements before diagnosis was associated with better survival. Whether this is due to beneficial effects of supplements, or differences between supplement users and non-users cannot be determined,” wrote the researchers, led by Guri Skeie from the University of Tromso.
“More research is needed to understand the interplay between nutrients, whether in food or supplements and cancer survival.”
The study also indicated that the benefits of supplement use may even extend beyond lung cancer. The use of cod liver oil and other supplements was associated with improved survival statistics for people with any kind of solid tumour, including breast and colorectal cancer.
“Given that randomized controlled trials have demonstrated no effects or increased incidence of lung cancer in supplementation studies in well-nourished populations, our results may be somewhat surprising,” wrote the researchers. “However, these studies used pharmacological doses of specific nutrients, and cannot easily be compared with ours.”
Diet and supplement use was established for the 68.518 participants of the Norwegian Women and Cancer study using a food frequency questionnaire. The most common supplement used was cod liver oil, said the researchers, followed by multivitamin and mineral supplements.
After adjusting the data to account for smoking status, the age at which the participants were diagnosed, and the stage of the cancer, Skeie and his co-workers report that consumption of cod liver oil daily for a year prior to diagnosis was associated with a 23 per cent reduction in the risk of death in patients with solid tumours, and a reduction of 44 per cent in lung cancer patients.
Additionally, daily and occasional use of other dietary supplements was associated with 30 and 45 per cent reduction, respectively, in the risk of death among lung cancer patients.
“When use of cod liver oil and other dietary supplements were combined into one variable daily use of both cod liver oil and other dietary supplements was associated with improved survival in lung cancer patients,” added Skeie.
Before or after?
Commenting on their study design, the researchers noted: “If the most relevant period for supplementation is after diagnosis, it is likely that our results underestimate the effect of supplementation, as some of the patients most likely have initiated supplementation.
“On the other hand, if a certain level of the nutrients or long-term supplementation is required for an effect, dietary supplement use before diagnosis might be more relevant for the association with survival.
“And if dietary supplement use only is an indicator of a set of health behaviours or beliefs, prediagnosis use might be more important, as these characteristics probably are stronger in those who already take supplements before diagnosis, than in those who initiate use afterwards.”
The researchers called for more research to study the apparent benefits of supplement use for survival chances in people with solid tumours.
“In countries where dietary supplement use is common, analyses of survival in cancer patients, particularly lung cancer patients, should take dietary supplement use into account,” they concluded.
Source: International Journal of Cancer
Volume 125, Pages 1155-1160
"Cod liver oil, other dietary supplements and survival among cancer patients with solid tumours"
Authors: G. Skeie, T. Braaten, A. Hjartaker, M. Brustad, E. Lund