Vegetable-rich diet may not protect against CVD
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A high level of vegetable consumption was not independently associated with reduced risk for CVD, according to results from a cohort study of nearly 400,000 participants.
The association between a vegetable-rich diet and reduced CVD risk was confounded by other variables, according to the researchers.
“Our large study did not find evidence for a protective effect of vegetable intake on the occurrence of CVD,” Qi Feng, PhD, researcher in the Nuffield department of population health at the University of Oxford, U.K., said in a press release. “Instead, our analyses show that the seemingly protective effect of vegetable intake against CVD risk is very likely to be accounted for by bias from residual confounding factors, related to differences in socioeconomic situation and lifestyle.”
Feng and colleagues analyzed 399,586 participants (mean age, 56 years; 55% women) from the UK Biobank cohort who did not have CVD at baseline.
Among the cohort, the mean intake of raw vegetables was 2.3 tablespoons per day and the mean intake of cooked vegetables was 2.8 tablespoons per day. Participants were followed for a median of 12.1 years, during which there were 18,052 CVD events and 4,406 CVD deaths.
Vegetables and CVD risk
Before adjustment for confounders, being in the highest quartile of total vegetable intake conferred reduced risk for incident CVD compared with being in the lowest quartile (HR = 0.9; 95% CI, 0.83-0.97), whereas for raw vegetable intake, the highest quartile was associated with reduced risk for CVD (HR = 0.89; 95% CI, 0.83-0.95) and MI (HR = 0.88; 95% CI, 0.81-0.96) compared with the lowest quartile, according to the researchers. There was no association between cooked vegetable intake and CVD risk (HR = 1; 95% CI, 0.91-1.09), and there was no association between total, raw or cooked vegetable intake and stroke risk.
Also, before adjustment for confounders, higher raw vegetable intake was associated with reduced risk for CVD mortality (HR = 0.85; 95% CI, 0.74-0.97), but higher cooked vegetable intake was not (HR = 0.96; 95% CI, 0.8-1.13), the researchers wrote.
Confounders attenuate association
However, the associations were substantially attenuated after adjustment for confounders; those confounders reduced the likelihood ratio chi-square statistic for association between raw vegetable intake and CVD incidence by 82% and between raw vegetable intake and CVD mortality by 87%, the researchers wrote.
“Adjustment for socioeconomic (including educational attainment and Townsend deprivation index) and lifestyle factors (including physical activity, smoking, drinking, use of mineral supplements, use of vitamin supplements, fruit intake, oily fish intake, non-oily fish intake, red meat intake and processed meat intake) results in most of the reductions in [likelihood ratio chi-square] statistic, while further adjustment for BMI and baseline health status resulted in only slight further reductions, suggesting that the observed associations are likely to be accounted for by residual confounding from socioeconomic status and lifestyle factors,” Feng and colleagues wrote.
Ben Lacey, MBChB, MSc, DPhil, FFPH, associate professor of epidemiology and public health at the University of Oxford and head of the UK Biobank Epidemiology Group, said in the release that the study has “implications for understanding the dietary causes of CVD and the burden of CVD normally attributed to low vegetable intake. However, eating a balanced diet and maintaining a healthy weight remains an important part of maintaining good health and reducing risk of major diseases, including some cancers. It is widely recommended that at least five portions of a variety of fruits and vegetables should be eaten every day.”
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