A new collaborative study suggests that consuming a diet rich in vegetables does not lower cardiovascular disease risk.
Performed by researchers from the Nuffield Department of Population Health at the University of Oxford, the Chinese University of Hong Kong, and the University of Bristol, the novel investigation found that although vegetable intake is vital for maintaining a balanced diet and avoiding a plethora of diseases, it does not lower cardiovascular disease risk.
Vegetables comprise properties such as carotenoids and alpha-tocopherol that could protect against cardiovascular disease; however, evidence from previous studies has been varied and unable to establish an association between vegetable intake and reduced cardiovascular disease risk.
Now, researchers have employed extensive data from the UK Biobank to assess how consuming cooked or uncooked vegetables can affect the risk of developing cardiovascular disease and explain how previous confounding factors may have impacted previous spurious results.
Professor Naomi Allen, UK Biobank’s chief scientist and co-author on the study, commented: “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.”
The findings of the study are published in Frontiers in Nutrition.
Analysing vegetable intake
The UK Biobank examines the health of around half a million UK adults through their healthcare records; participants were enrolled between 2006 and 2010 and were interviewed about their diet, lifestyle, medical and reproductive history, and other factors. For their study, the team utilised the enrolment responses of 399,586 individuals, of which 4.5% went on to develop cardiovascular disease, looking at their average daily consumption of uncooked versus cooked vegetables.
The team assessed the association with the risk of hospitalisation or death from myocardial infarction, stroke, or major cardiovascular disease, controlling for a wide range of potential confounding factors, including socioeconomic status, physical activity, and other dietary factors. Moreover, the team analysed the potential role of residual confounding, which is whether unknown factors or an inaccurate measure of known factors may create an incorrect statistical association between cardiovascular disease risk and vegetable intake.
Impacts on cardiovascular disease risk
The mean daily intake of total vegetables, raw vegetables, and cooked vegetables were 5.0, 2.3, and 2.8 heaped tablespoons per person, respectively. The risk of dying from cardiovascular disease was 15% lower for participants with the highest intake of vegetables. However, this beneficial effect was lessened when considering potential confounding factors such as socioeconomic, nutritional, and health- and medicine-related.
Controlling these factors reduced the predictive statistical power of vegetable consumption on reducing cardiovascular disease risk by 80%. This suggests that more precise measures of these confounders would have illuminated any residual effect of vegetable intake.
Dr Qi Feng, a researcher at the Nuffield Department of Population Health at the University of Oxford, and 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 team stated that future studies should look to evaluate whether specific types of vegetables affect cardiovascular disease risk.
Dr Ben Lacey, Associate Professor in the department at the University of Oxford, concluded: “This is an important study with 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 the 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.”
