Vegetable Intake Does Not Reduce Cardiovascular Risk, Study Finds
A long-term study on almost 400 000 people in the UK finds little or no evidence that differences in the amount of vegetables consumed affects the risk of cardiovascular disease.
When known socio-economic and lifestyle confounding factors are corrected for, the small apparent positive effect that remains could likely also be explained away by further confounders.
Getting enough vegetables is important for maintaining a balanced diet and avoiding a wide range of diseases. But might a diet rich in vegetables also lower the risk of cardiovascular disease (CVD)? Unfortunately, new results from a powerful, large-scale new study study in Frontiers in Nutrition found no evidence for this.
The notion of CVD risk being lowered by vegetable consumption might seem plausible at first, as their ingredients such as carotenoids and alpha-tocopherol (vitamin E) have properties that could protect against CVD. But so far, prior evidence for an overall effect of vegetable consumption on CVD has been inconsistent.
The study, which drew on UK Biobank data, found a higher consumption of cooked or uncooked vegetables is unlikely to affect the risk of CVD. The study authors also explained how confounding factors might explain previous spurious, positive findings.
“The UK Biobank is a large-scale prospective study on how genetics and environment contribute to the development of the most common and life-threatening diseases. Here we make use of the UK Biobank’s large sample size, long-term follow-up, and detailed information on social and lifestyle factors, to assess reliably the association of vegetable intake with the risk of subsequent CVD,” said Prof Naomi Allen, UK Biobank’s chief scientist and co-author on the study.
The UK Biobank, follows the health of half a million adults in the UK by linking to their healthcare records. Upon their enrolment in 2006-2010, these volunteers were interviewed about their diet, lifestyle, medical and reproductive history, and other factors.
The researchers used the responses at enrolment of 399 586 participants (of whom 4.5% went on to develop CVD) to questions about their daily average consumption of uncooked versus cooked vegetables. They analysed the association with the risk of hospitalization or death from myocardial infarction, stroke, or major CVD. They controlled for a wide range of possible confounding factors, including socio-economic status, physical activity, and other dietary factors.
Crucially, the researchers also assessed the potential role of ‘residual confounding’, that is, whether unknown additional factors or inaccurate measurement of known factors might lead to a spurious statistical association between CVD risk and vegetable consumption.
The mean daily intake of total vegetables, raw vegetables, and cooked vegetables was 5.0, 2.3, and 2.8 heaped tablespoons per person. The risk of dying from CVD was about 15% lower for those with the highest intake compared to the lowest vegetable intake. However, this effect was greatly weakened when possible confounding factors were taken into account. Controlling for factors such as socio-economic status reduced the predictive statistical power of vegetable intake on CVD by over 80%, suggesting that more precise measures of these confounders would have explained away any residual effect of vegetable intake.
Dr Qi Feng, the study’s lead author, said: “Our large study did not find evidence for a protective effect of vegetable intake on the occurrence of CVD. 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.”
The researchers suggest that subsequent studies should further assess whether particular types of vegetables or their method of preparation might affect the risk of CVD.
Source: Frontiers
