Background Although high fruit and vegetable intakes and high vitamin C intake may protect against type 2 diabetes risk, recent evidence in adults has suggested that circulating vitamin C levels, rather than fruit and vegetable intake, could be particularly important. However, the influence of these factors on emerging type 2 diabetes risk in childhood (particularly insulin resistance) has not been reported. We therefore examined these associations in children, including their contributions to emerging ethnic differences in insulin resistance.

Methods This investigation is based on a cross-sectional, school-based survey in UK children aged 9–10 years, predominantly of white European, South Asian and black African origin from London, Birmingham and Leicester. Children provided a detailed 24-hour dietary recall (collected by a trained nutritionist) providing intakes of fruit, vegetables and vitamin C, had detailed measurements of body composition and provided a fasting blood sample for measurements of plasma vitamin C, serum insulin, plasma glucose, HbA1c and other metabolic markers; homeostasis model assessment (HOMA) insulin resistance was also derived. Multilevel linear regression models were fitted to provide adjusted means and differences in risk factors.

Results Among 2025 participants (68% response rate), intakes of fruit, vegetables and vitamin C showed no associations with markers of insulin resistance, though plasma vitamin C showed an inverse association. In age, gender, month, adiposity and school adjusted analyses, a 1 interquartile range increase in plasma vitamin C level was associated with 9.22% (95% CI 6.25, 12.11%) lower HOMA insulin resistance, 0.75% (95% CI 0.32, 1.18%) lower fasting glucose, a 4.11% (95% CI 2.78, 5.42%) lower urate and 2.26% (95% CI 1.03, 3.51%) higher HDL-cholesterol and (less consistently) a 0.62% (95% CI 0.24, 1.0%) higher HbA1c. Further adjustments for socio-economic status and physical activity did not substantially alter the results. Plasma vitamin C levels were markedly lower among South Asian children; higher levels of HOMA insulin resistance in South Asian children (particularly in Bangladeshis) could be at least partly accounted for (˜20%) by lower plasma vitamin C levels.

Conclusion Plasma vitamin C levels (but not fruit, vegetable or vitamin C intakes) are independently associated with insulin resistance in childhood, a consistent pattern to what has been shown in adult studies. Further studies are needed to establish whether this association is causal and can provide a basis for type 2 diabetes prevention.