Hannah Roeder, MD, MPH
In the health care community, we continuously search for the best diet to prevent vascular disease. The authors investigated whether greater peanut consumption, as recorded in a food frequency questionnaire in the Japan Public Health Center-based Prospective Study, was correlated with lower rates of stroke and heart disease among middle-aged Japanese men and women. More than 70,000 participants aged 45 to 74 years completed food frequency questionnaires, and the participants were monitored for a median follow-up of 14.8 years. The authors calculated multivariable hazard ratios for the highest versus lowest quartiles of peanut consumption (after adjusting for some demographic features, medical co-morbidities, and dietary factors). Hazard ratios were 0.84 (95% CI: 0.77-0.93) for total stroke, 0.80 (0.71-0.90) for ischemic stroke, 0.93 (0.79-1.08) for hemorrhagic stroke, 0.97 (0.80-1.17) for ischemic heart disease, and 0.87 (0.80-0.94) for cardiovascular disease (defined as stroke and heart disease). The authors concluded that higher peanut consumption was associated with reduced risk of stroke, particularly ischemic stroke, but not ischemic heart disease. The authors proposed that the high level of unsaturated fatty acids improving lipid profiles and lowering blood pressure contributes to the beneficial effects.
The study suffers from many of the limitations common to nutritional epidemiology research. A big weakness of this study is that food frequency questionnaires may not reflect actual dietary intake. In this particular instance, the authors cite prior research1 showing nut intake from 28-day dietary records had only a negligible to low positive correlation with the reported nut intake from the food frequency questionnaire (Spearman correlation of 0.25 in men and 0.19 in women). Additionally, low and high peanut eaters had many baseline differences, with peanut eaters being younger, more active, and less likely to have hypertension, diabetes, and tobacco use. Although the investigators controlled for many relevant variables, including adjustment for a modified DASH dietary pattern, the groups likely have other differences that were not controlled for and act as confounders, particularly since peanuts are not a traditional element of a Japanese diet.
While the research question and data are intriguing, the study limitations are significant, so grab a handful of peanuts to snack upon if you prefer, but concluding they protect against stroke may be premature.
References:
- Nanri A, Shimazu T, Ishihara J, Takachi R, Mizoue T, Inoue M, Tsugane S; JPHC FFQ Validation Study Group. Reproducibility and validity of dietary patterns assessed by a food frequency questionnaire used in the 5-year follow-up survey of the Japan Public Health Center-Based Prospective Study. J Epidemiol. 2012;22:205–215.
