A diet rich in omega-3 fatty acids, dietary fiber, beta-carotene and vitamin E offers significant protection against non-Hodgkin lymphoma, says a Swedish-Danish-American study.
The researchers behind the new study, led by Ellen Chang from the Northern California Cancer Center, looked at the dietary intakes of 591 people with non-Hodgkin lymphomas (NHL) and certain lymphoma subtypes, and 460 healthy controls recruited from seven Swedish counties.
“Overall, we found that eating fish and marine fats was associated with lower risk of overall non-Hodgkin lymphomas and certain lymphoma subtypes (which should be examined separately, since NHLs represent a group of several different lymphomas),” Dr. Chang said. “We also found that consuming certain antioxidant vitamins, commonly found in some fruits and vegetables, was associated with lower risk of overall NHL and some common subtypes.”
Non-Hodgkin Lymphoma is a cancer that starts in the lymphatic system and encompasses about 29 different forms of lymphoma. According to the American Cancer Society, over 50,000 new cases are diagnosed in the US every year.
The participants were recruited between 2000 and 2002, and dietary assessments were performed using a validated, semi-quantitative 137-item (including supplements) food frequency questionnaire (FFQ). The researchers assumed that recent dietary habits had not changed significantly since the distant past.
After adjusting the results to eliminate potential confounding factors like gender and BMI, Chang and her colleagues report that, while dietary intake of most macronutrients was not associated with NHL risk, average consumption of about 0.8 grams per day (0.4 grams per 1,000 kcal) of omega-3 fatty acids was associated with a 20 and 60 per cent reduced risk of NHL and its subtypes, compared to those who consumed about 0.2 grams per day. This also extended to fish oil supplements, with people who supplemented their diet with fish oil at a significantly reduced risk of NHL and its subtypes than people who did not take the supplements (risk reduction of between 30 and 50 per cent).
Strong associations between dietary fiber intake and NHL risk reductions were also observed, said the researchers in the American Journal of Epidemiology. Indeed, Daily average intake of 14.4 grams per 1,000 kcal was linked to a 50 to 60 per cent risk reduction of NHL and all its subtypes.
Dietary consumption of the micronutrients beta-carotene or alpha-tocopherol was also associated with lower NHL risk, said the researchers, with the highest dietary beta-carotene intake (average 4.4 micrograms per day) associated with 40 per cent reduction in NHL risk, compared to the lowest intake (average 1.2 micrograms per day). Similarly, the highest dietary alpha-tocopherol intake (average 9.8 milligrams per day) associated with 60 per cent reduction in NHL risk, compared to the lowest intake (average 5.0 milligrams per day).
Dr. Chang said, however, that some micronutrients were associated with an increased NHL risk: “We found that consuming calcium and retinol was associated with higher risk of NHL and its most common subtypes. We hypothesize that the latter finding may be because calcium and retinol block the formation of biologically active, hormonal vitamin D in the body, and we previously found that exposure to sunlight—which is the primary source of vitamin D for many people-- was associated with lower NHL risk (see Smedby et al., J Natl Cancer Inst 2005).
“Therefore, higher levels of vitamin D may protect against NHL risk, whereas lower levels of vitamin D may increase NHL risk,” she said.
The mechanism of the apparent protective effects of the nutrients was not investigated by the researchers, but they propose that nutrients which affect inflammation, vitamin D activity, oxidative DNA damage, or DNA methylation could be associated with NHL risk.
The study does have several limitations, the researchers noted, including the limited sample size, and the assumption that dietary patterns did not change significantly over time.
“Of course, these findings need to be replicated elsewhere, ideally in studies where diet is measured in a large group of healthy people, who are then followed over many years to find out who develops NHL later on,” said Chang.
E.T. Chang, K.M. Bälter, A. Torrång, K. Ekström Smedby, M. Melbye, C. Sundström, B. Glimelius and H-O. Adami. Nutrient Intake and Risk of Non-Hodgkin's Lymphoma; American Journal of Epidemiology. Dec 2006; Volume 164, Issue 12, Pages 1222-1232; doi:10.1093/aje/kwj330