Research Question, Study Population, and Design
To begin with, the research question that the article’s authors were concerned with was the following: To what extent, if any, can variety and quantity in vegetable and fruit intake affect the risk of coronary heart disease (CHD) over a long period of time? According to Bhupathiraju et al. (2013), the Nurses’ Health Study (NHS), initiated in 1976, and the Health Professionals Follow-Up Study (HPFS), which began in 1986, included 121,701 female registered nurses and 51,529 male health professionals, respectively. However, for the current intervention, the populations were reduced to 42,135 men and 71,141 women. Lastly, this was a prospective cohort study, and it is possible to say that the design and population are appropriate to address the research question. The former leads to informative and relevant findings, while the samples were large enough to represent the whole population, including non-healthcare professionals.
Dietary Assessment Method and Data Collection
A dietary assessment method selected for the investigation was a food-frequency questionnaire (FFQ). Thus, “the FFQ asked participants to report their usual intake (never to ≥6 times/d /d/d) of a standard portion size (eg, 0.5 cups strawberries, one banana, 0.5 cups cooked spinach) of fruit and vegetables” (Bhupathiraju et al., 2013, p. 1515). Unfortunately, the researchers failed to indicate how the data were collected, only mentioning that the questionnaires were sent to the participants every 4 years. Therefore, it is likely that the participants received the form via either mail or computer. These two methods are considered quite effective but might have higher non-response rates.
Main Dietary Exposure
One may say there were no dietary exposures, as the participants could eat whatever they wanted. In their FFQs, they had to report the variety and quantity of their fruit and vegetable intake, which were the factors that the article’s authors considered. Bhupathiraju et al. (2013) indicate that they specifically divided the digested fruits and vegetables into “citrus fruit, green leafy vegetables, cruciferous vegetables, and fruit and vegetables rich in β-carotene, lutein, lycopene, or vitamin C” (p. 1515). They also excluded fruit juice, legumes, and potatoes.
Outcome
The study’s outcome is that a higher quantity of fruit and vegetable intake results in a significantly decreased risk of developing CHD, and consumption of specific vegetable and fruit subgroups also lowers the risk, but not severely. Researchers conducted thorough analyses and interpretations after receiving the required data to assess this outcome.
Time Frame Between the Exposure and Outcome
The study involved two different populations, so the time frame was 24 years for women participating in the NHS and 22 years for men participating in the HPFS. At the beginning of the paper, the authors mention that their prior research had a time frame of 8-14 years, and valuable results were achieved (Bhupathiraju et al., 2013). It is possible to say that more than two decades are enough to assess the effects of fruit and vegetable intake on participants’ health.
Statistical Analyses and Measures of Association
The authors used multivariable analyses and adjusted for non-dietary and dietary covariates. It is noticeable that “Cox proportional hazard models with time-varying covariates with age as the time scale were used for all analyses,” and Bhupathiraju et al. (2013) also conducted numerous sensitivity analyses (p. 1516). Measures of association were fruit and vegetable variety, quantity intake, and cases of CHD diagnosis or death.
The authors ensured that different external factors affecting the exposure variable were considered in their analysis. Confounders included smoking status, BMI, menopausal status, physical activity, hormone therapy, parental history of CHD, alcohol intake, and multivitamin use. Including a sleeping schedule confounder would also be essential because it can severely affect a person’s health.
Major Results and Their Interpretations
This study’s key result is that quantity is more associated with CHD risk reduction than variety. An additional outcome is that the risk of CHD reduces linearly for intakes up to approximately five servings per day, but having more fruit and vegetable intakes does not provide additional protection. Interestingly, “each increase of one serving per day in fruit and vegetable intake, overall, was associated with a 3% lower risk of CHD,” and consuming 4.0 to 4.9 servings per day allows for a reduction in CHD risk by 16% (Bhupathiraju et al., 2013, pp. 1521-1522). The authors’ interpretations of the results seem reasonable because they conducted additional sensitivity analyses, which proved the validity and consistency of the findings.
Thinking Critically About the Results
When critically analyzing the study, one may notice that there is a likelihood of potential bias in how dietary exposures were measured, including random and non-random biases. First, considering that diet was self-reported by the participants and assessed by FFQs, it is possible that not all reports were sincere or accurate (Bhupathiraju et al., 2013). In case some participants of the study faked their fruit and vegetable intakes in the questionnaire due to not having time to report them accurately or because of other factors, this might have affected the findings and their interpretation.
Further, the authors indicate that not all confounders were considered. According to other studies, such as an article by Huang et al. (2022), poor sleep patterns or a prolonged lack of sleep are associated with an increased risk of CHD, so referring to this confounder would be more efficient. Thus, results will be interpreted while considering the impact of sleep, making them more accurate. Other than that, there are no additional considerations regarding the dietary assessment or the analysis to propose.
Relevant Bradford Hill Criteria
In this study, there is moderate strength of association because no association was found between fruit and vegetable variety and CHD, and the one identified between quantity and the disease risk was nonlinear. The second relevant Bradford Hill criterion is consistency, and the authors note that their results are similar to their previous investigations and other researchers’ results (Bhupathiraju et al., 2013).
The paper has a strong and evident biological plausibility. For instance, it is proven by biologists that vitamin C, which is found in some fruits and specifically noted by Bhupathiraju et al. (2013), has beneficial effects on one’s cardiovascular system. Bhupathiraju et al. (2013) also indicate that “the existence of strong biological mechanisms makes these associations plausible” (p. 1522-1523). These are the most relevant Bradford Hill Criteria to be applied to the paper to prove its value and contribution.
Policy Implications
Lastly, one can draw some important policy implications from this paper. For instance, it may be beneficial for nutrition policies to refer to the findings of Bhupathiraju et al. (2013) because including more fruit and vegetable intakes in people’s meals will eventually improve the nation’s health. Secondly, health and food education policies also need to apply the paper’s results when spreading awareness about the benefits of fruits and vegetables.
References
Bhupathiraju, S. N., Wedick, N. M., Pan, A., Manson, J. E., Rexrode, K. M., Willett, W. C., Rimm, E. B., & Hu, F. B. (2013). Quantity and variety in fruit and vegetable intake and risk of coronary heart disease. The American Journal of Clinical Nutrition, 98(6), 1514-1523. Web.
Huang, B. H., Duncan, M. J., Cistulli, P. A., Nassar, N., Hamer, M., & Stamatakis, E. (2022). Sleep and physical activity in relation to all-cause, cardiovascular disease and cancer mortality risk. British Journal of Sports Medicine, 56(13), 718-724. Web.