Postprandial glycaemic response in different ethnic groups in East London and its association with vitamin D status: study protocol for an acute randomised crossover trial

In the UK, black African-Caribbeans (ACs) and South Asians (SAs) have 3-6 times greater risks of developing diabetes than white Caucasians do. East London is among the areas with the highest prevalence of type 2 diabetes and the highest proportion of minority groups. This ethnic health inequality is ascribed to socioeconomic standing, dietary habits, culture, and attitudes, while biological diversity has rarely been investigated. The evidence shows that the postprandial glucose peak values in SAs are 2-3 times greater than those in white Caucasians after the same carbohydrate loads; however, the mechanism is poorly understood. In the UK, 50% of SAs and 33% of ACs have vitamin D (vitD) deficiency, whereas 18% of white Caucasians have vitamin D deficiency. There is evidence that vitD status is inversely associated with insulin resistance in healthy adults and diabetic patients and that vitD supplementation may help improve glycaemic control and insulin resistance in type 2 diabetes patients. However, little evidence is available on minority groups or East London. This study will investigate the postprandial glycaemic response (PGR) in three ethnic groups (white Caucasians, SAs and ACs) in East London and link PGR to plasma 25(OH)D (an indicator of vitD status). Ninety-six healthy adults (n=32 per group) will be recruited. Two test drinks will be provided to the participants (300 ml of glucose drink containing 75 g glucose, and 300 ml of pure orange juice) on different occasions. PGR is monitored before and after drinking every 30 min for up to 2 hours via finger prick. A fasting blood sample obtained via phlebotomy will be used for 25(OH)D and relevant tests. A knowledge/perception questionnaire about vitD and a 4-day food diary (analysing vitD dietary intake) will also be collected. The findings of the study will be shared with participants, published in journals, disseminated via social media, and used to inform a randomized controlled trial of the effects of vitD supplementation on PGR in minority groups. The study complies with the Helsinki Declaration II and was approved by the Senate Research Ethics Committee at City, University of London (ETH2223-2000). The study findings will be published in open access peer-reviewed journals and disseminated at national and international conferences. ClinicalTrials.gov Identifier: NCT06241976