‘Five a day’ fruits and vegetables
Only one previous small published study from the United Kingdom has examined how blood levels of vitamin C and carotenoids are associated with incident type 2 diabetes, Dr. Zheng and colleagues wrote.
They investigated the relationship in 9,754 adults who developed new-onset type 2 diabetes and a comparison group of 13,662 adults who remained diabetes free during an average 9.7-year follow-up, from 340,234 participants in the European Prospective Investigation Into Cancer and Nutrition–InterAct study.
Participants were from Denmark, France, Germany, Italy, the Netherlands, Spain, Sweden, and the United Kingdom, and incident type 2 diabetes occurred between 1991 and 2007.
The researchers used high-performance liquid chromatography–ultraviolet methods to determine participants’ plasma levels of vitamin C and six carotenoids (alphta-carotene, beta-carotene, lycopene, lutein, zeaxanthin, beta-cryptoxanthin), which they used to calculate a composite biomarker score.
The recommendation to eat at least five fruits and vegetables a day corresponds to eating ≥400 g/day, according to Dr. Zheng and colleagues. The self-reported median fruit and vegetable intake in the current study was 274, 357, 396, 452, and 508 g/day from lowest to highest quintile.
After multivariable adjustment, higher levels of plasma vitamin C and carotenoids were associated with an 18% and 25% lower risk of incident type 2 diabetes per standard deviation, respectively.
Compared with patients whose vitamin C and carotenoid composite biomarker scores were in the lowest 20%, those with scores in the top 20% had half the risk of incident diabetes. Increasing fruit and vegetable consumption by 66 g/day was associated with a 25% lower risk of developing diabetes.
“These findings provide strong evidence from objectively measured biomarkers for the recommendation that fruit and vegetable intake should be increased to prevent type 2 diabetes,” according to the researchers.
However, consumption of fruits and vegetables remains far below guideline recommendations, they observed. “Although five portions a day of fruit and vegetables have been recommended for decades, in 2014-2015, 69% of U.K. adults ate fewer than this number, and this proportion is even higher in European adults (86%).”
Dr. Zheng and colleagues acknowledged that study limitations include those that are inherent with observational studies.
Although they could not distinguish between juice, fortified products, or whole foods, the analyses “were adjusted for vitamin supplement use, and suggest that as biomarkers of fruit and vegetable intake these findings endorse the consumption of fruit and vegetables, not that of supplements,” they maintained.
The study by Mr. Hu and colleagues was funded by the National Institutes of Health. The InterAct project was funded by the EU FP6 program. Biomarker measurements for vitamin C and carotenoids were funded by the InterAct project, EPIC-CVD project, MRC Cambridge Initiative, European Commission Framework Program 7, European Research Council, and National Institute for Health Research. Dr. Zheng has reported receiving funding from Westlake University and the EU Horizon 2020 program.
A version of this article originally appeared on Medscape.com.