Adequate vitamin E, C, and beta-carotene intake reduces risk of type 2 diabetes

In a recent study published in advances in nutrition, researcher To examine the effects of vitamins C and E and beta-carotene on the risk of type 2 diabetes (T2D).

study: Vitamins C, E, and beta-carotene and risk of type 2 diabetes: a systematic review and meta-analysis. Image credit: Suriyawut Suriya / Shutterstock.com

About research

Previously published meta-analyses have discussed the protective effects of β-carotene and vitamin E, but not vitamin C, on the development of T2D. Furthermore, these analyzes did not focus on randomized controlled trials (RCTs) or dose-response relationships.

For the current review, all relevant information was retrieved from Embase, MEDLINE, and the Cochrane Library databases. Case-cohort, cohort, nested case-control, and RCT studies were considered to investigate the relationship between dietary intake, circulating levels of vitamin C, vitamin E, and β-carotene and T2D incidence. Studies written in languages ​​other than English were not included in the review.

The initial search retrieved a total of 6,190 articles, of which 40 met eligibility criteria and were considered. Both observational and RCT studies showed low, moderate, or severe risk of bias.

Meals and T2D

T2Dis is associated with β-cell dysfunction and insulin resistance and is one of the most common and globally prevalent metabolic diseases. Several strategies related to weight loss, diet, and physical activity have been devised to reduce the risk of T2D.

Adhering to certain dietary patterns, such as the Mediterranean diet, definitely reduces the risk of T2D. The Mediterranean diet emphasizes increasing intake of fruits, vegetables, olive oil, and fish, as well as minimizing intake of highly processed foods and meat-based products. Fruits and vegetables are rich in antioxidants such as vitamin E, vitamin C, and beta-carotene, which have many beneficial biological effects.

Vitamin C is a water-soluble vitamin found in vegetables and fruits that regenerates vitamin E from its oxidized form. Vitamin E is a fat-soluble vitamin found in seeds, nuts, and vegetable oils that protects cell membranes from lipid peroxidation. Additionally, beta-carotene is a provitamin A carotenoid commonly found in fruits and vegetables.

Antioxidants protect cells from oxidative stress caused by the release of free radicals. Oxidative stress increases insulin resistance by inducing inflammatory processes and suppressing insulin signaling.

Several studies have shown that high levels of dietary antioxidants may reduce insulin resistance and T2D. Therefore, it is important to understand the mechanisms that contribute to each vitamin’s antioxidant properties.

How do beta-carotene, vitamin C, and vitamin E affect T2D risk?

Dietary intake of vitamin C, vitamin E, and beta-carotene has been shown to reduce the risk of T2D. However, this association is nonlinear and plateaus at moderate intakes.

Vitamin C is inversely related to insulin resistance. To date, few studies have revealed the effects of vitamin C on β-cell function.

Among the RCT studies reviewed, there was not enough data to show that supplementation with these vitamins reduces the risk of T2D. In contrast to vitamin C and β-carotene, vitamin E supplementation was associated with insulin resistance.

Nevertheless, a nonlinear dose-response gradient was observed, showing that the lowest risk of diabetes was associated with moderate intake of dietary vitamins. According to Nordic guidelines, the acceptable dietary intake of vitamin C is 75 mg and 90 mg per day for men and women, respectively. The recommended amount of vitamin E intake is 8 to 15 mg per day for both men and women.

These recommendations can be achieved by consuming half a cup of red pepper and half a cup of almonds each for vitamins C and E. Although a reference value for beta-carotene has not been established, consuming 3 to 6 mg per day may reduce the risk of chronic disease.

Mendelian randomization (MR) analysis did not show a genetically predicted causal relationship between circulating vitamin E, vitamin C, or β-carotene and T2D symptoms. This finding was also supported by RCT data that revealed that supplementation with these antioxidants provided no additional benefit in reducing the risk of T2D in healthy adults.

Vitamin C, vitamin E, and beta-carotene work synergistically to suppress oxidative stress, so taking them individually may not have any beneficial effects. A person who follows a Mediterranean diet consumes adequate amounts of antioxidants, which work synergistically to reduce her risk of T2D.

conclusion

Consuming enough, but not too much, vitamin C, vitamin E, and beta-carotene can prevent the risk of T2D in healthy adults. Therefore, these vitamin supplements should not be used as a preventive strategy to reduce T2D in healthy people.

However, future research is needed to identify the threshold levels of antioxidants in smokers and those genetically predisposed to diabetes for optimal effectiveness.