Vitamin C Linked to Lower Risk for Type 2 Diabetes 

Higher plasma vitamin C level and, to a lesser degree, fruit and vegetable intake, are associated with a decreased risk for type 2 diabetes by 62 percent, according to the results of a population-based, prospective cohort study reported in the July 28 issue of the Archives of Internal Medicine. Correlating blood levels of vitamin C and diabetes, the researchers found that men and women with the highest blood levels (at least 1.10 and 1.29 mg/dL, respectively) had a 62 per cent reduction in their risk of developing type-2 diabetes, compared to men and women with the lowest blood levels (less than 0.56 and 0.77 mg/dL, respectively).

One key dietary recommendation to prevent chronic disease is to eat at least 5 servings of fruits and vegetables daily, but evidence for this protective effect against type 2 diabetes has been inconclusive. Plasma vitamin C level is a good biomarker of fruit and vegetable intake that can be used to assess the risk for diabetes because in Western populations, approximately 90% of vitamin C is obtained from this source.

This is a prospective, population-based cohort study to examine the risk for type 2 diabetes and intake of fruits and vegetables and plasma vitamin C levels.

"Epidemiologic studies suggest that greater consumption of fruit and vegetables may decrease the risk of diabetes mellitus, but the evidence is limited and inconclusive," write Anne-Helen Harding, PhD, from the University of Cambridge, United Kingdom, and colleagues from the European Prospective Investigation of Cancer–Norfolk study. "Plasma vitamin C level is a good biomarker of fruit and vegetable intake, but, to our knowledge, no prospective studies have examined its association with diabetes risk. This study aims to examine whether fruit and vegetable intake and plasma vitamin C level are associated with the risk of incident type 2 diabetes."

From 1993 to 1997, a total of 21,831 healthy participants aged 40 to 75 years underwent baseline measurement of plasma vitamin C level and evaluation of habitual intake of fruit and vegetables with use of a semiquantitative food frequency questionnaire. Between February 1993 and the end of December 2005, there were 735 clinically incident cases of diabetes diagnosed during 12 years of follow-up.

Plasma vitamin C level was strongly inversely associated with diabetes risk. After adjustment for demographic, lifestyle, and anthropometric variables, the odds ratio (OR) of diabetes in the top quintile of plasma vitamin C was 0.38 (95% confidence interval [CI], 0.28 – 0.52). Adjusted OR of diabetes in the top quintile of fruit and vegetable intake was 0.78 (95% CI, 0.60 – 1.00).

"Higher plasma vitamin C level and, to a lesser degree, fruit and vegetable intake were associated with a substantially decreased risk of diabetes," the study authors write. "Our findings highlight a potentially important public health message on the benefits of a diet rich in fruit and vegetables for the prevention of diabetes."

The study authors write. "The strong independent association observed in this prospective study, together with biological plausibility, provides persuasive evidence of a beneficial effect of vitamin C and fruit and vegetable intake on diabetes risk. Because fruit and vegetables are the main sources of vitamin C, the findings suggest that eating even a small quantity of fruit and vegetables may be beneficial and that the protection against diabetes increases progressively with the quantity of fruit and vegetables consumed."

The Cambridge-based researchers note that dietary fibre from the fruit and vegetables was not associated with a decrease risk of diabetes, despite previous studies reporting a protective effect from cereal fibre.

“The lack of association of fruit and vegetable fibre with diabetes risk but the protective effect of cereal fibre for diabetes risk reported in a recent meta-analysis is noteworthy and may suggest that it is not the fibre content of fruit and vegetables per se that contributed to the reduced risk for diabetes in our study,” wrote the researchers.

Practice Pearls:

• Plasma vitamin C levels are inversely associated with the risk for type 2 diabetes.
• There is an inverse association between fruit and vegetable intake and the risk for type 2 diabetes, with a greater effect for fruit intake.

Archives of Internal Medicine: Volume 168, Number 14, Pages 1493-1499
"Plasma Vitamin C Level, Fruit and Vegetable Consumption, and the Risk of New-Onset Type 2 Diabetes Mellitus – The European Prospective Investigation of Cancer – Norfolk Prospective Study"
Authors: A.-H. Harding, N.J. Wareham, S.A. Bingham, K. Khaw, R. Luben, A. Welch, N.G. Forouhi

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