Eating vegetables alone ‘not enough’ to reduce heart risk: study

Not according to researchers from the Nuffield Department of Population Health at the University of Oxford, the Chinese University of Hong Kong, and the University of Bristol.

They studied 399,586 participants via the UK Biobank, which follows the health of half a million adults in the UK by linking to their healthcare records. After they enrolled in 2006-2010, these volunteers were tracked over the next 12 years about their diet, lifestyle, medical and reproductive history, and other factors.

On average, people said they ate two heaped tablespoons of raw vegetables, three of cooked vegetables and five in total per day.

The study revealed the risk of dying from CVD was about 15% lower for those with the highest intake compared to the lowest vegetable intake.

However, this apparent effect was substantially weakened when possible socio-economic, nutritional, and health- and medicine-related confounding factors were taken into account.

Controlling for these factors reduced the predictive statistical power of vegetable intake on CVD by over 80%, suggesting that more precise measures of these confounders would have completely explained any residual effect of vegetable intake.

“In this study of 0.4 million middle-aged adults with 12-year follow-up, higher intakes of raw but not cooked vegetables were associated with lower CVD risk,”​ the study concluded. “However, given the large reductions in the predictive values of raw vegetable intake after adjustment for socioeconomic and lifestyle factors, residual confounding is likely to account for much, if not all, of the remaining associations.”​

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.”​

He suggested that future studies should further assess whether particular types of vegetables or their method of preparation might affect the risk of CVD.

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 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.”​