Asian Indians develop metabolic syndrome and diabetes earlier than in most population. In other words, Asian Indians have all the risk factors which may predispose to accelerated ageing; insulin resistance, dysglycemia, subclinical inflammation, and vasculopathy.

Vitamin D deficiency is widespread in both urban and rural populations of India. It is possible that vitamin D may also act on pathway related to aging which also are common to chronic diseases like diabetes. In this respect the surrogate markers of ageing (leukocyte telomerase length and telomerase activity) could be affected if vitamin D deficiency occurs. While some studies have shown relationship between vitamin D supplementation and leukocyte telomerase length in other populations, such study has not been systematically performed in Asian Indians. In this context, it is also not clear if some proposed genes of ageing may have some influence of development of prediabetes or diabetes and may interact with vitamin D. One of the candidate gene MSTN, according to our previous study, showed close correlation with excess body fat and decrease muscle mass, body composition characteristics conducive to development of diabetes. Additionally, deficiency of vitamin D could be linked to insulin resistance, prediabetes, though these issues have been debated. Some studies suggest that vitamin D supplementation may improve insulin sensitivity in Asian Indians. A research focusing on relationship of vitamin D supplementation with pro-ageing metabolic factors (glycemia, insulin resistance etc,), ageing related genes and surrogate markers of ageing is needed.

This study has two components; cross-sectional and prospective. Cross-sectional study will be of 2 years duration where 500 subjects from urban area of Delhi will be screened randomly for the vitamin D deficiency and its determinants including duration of sun exposure. The population will be representative of different socio-economic strata of the society. In this, vitamin D levels, leukocyte telomerase length and telomerase activity in peripheral blood leukocytes, telomerase activity and single nucleotide polymorphisms \[ACTN3, VDR, FOXO3A, SIRT1 and MSTN\] in prediabetes Asian Indians.

Second part consists of open-label randomized placebo-controlled prospective trial, in which the investigators would be enrolling 200 prediabetic subjects with vitamin D deficiency. These subjects will be randomized into two groups; lifestyle modification counseling along with intervention with either vitamin D or placebo. Anthropometry, body composition, levels of vitamin D, blood glucose (including oral glucose tolerance test) and dietary assessments will be assessed periodically (every 3 months). In those having recurrent vitamin D deficiency, the course of vitamin D will be repeated. Diet and exercise will be recommended as per the regular norms for overweight and obese subjects. Clinical and dietary profile, sunlight exposure, glycemic and lipid profile other metabolic parameters, body composition, hand grip strength, leukocyte telomerase length and telomerase activity will be assessed at enrolment time and one year intervention. As mentioned above, genes related to ageing will be evaluated. Appropriate statistical methods will be used to see effects of intervention with Vitamin D on metabolic state (particularly insulin resistance and glycemia) and leukocyte telomerase length and telomerase activity. Effects of polymorphisms of pro-ageing genes will be assessed