INADEQUATE VITAMIN-D STATUS - DOES IT CONTRIBUTE TO THE DISORDERS COMPRISING SYNDROME-X

Environmental factors are important in the aetiology of glucose intole rance, type II diabetes and IHD. The lack of vitamin D, which is neces sary for adequate insulin secretion, relates demographically to increa sed risk of myocardial infarction. These disorders are connected, dege nerative vascular disease increasing with glucose intolerance and diab etes and, with its risk factors, comprising syndrome 'X'. Evidence is presented suggesting that vitamin D deficiency may be an avoidable ris k factor for;syndrome 'X', adding another preventative measure to curr ent recommendations which are aimed at reducing the worldwide epidemic of these disorders. Experimentally, vitamin D deficiency progressivel y reduces insulin secretion; glucose intolerance follows and becomes i rreversible. Relationships between vitamin D status, glucose tolerance and 30 min insulin secretion during oral glucose tolerance tests are reported in British Asians; insulin secretion, but not glycaemia, impr oving with short-term supplementation. Studies showing reduction in bl ood pressure and in risk of heart attack and diabetes with exercise (u sually outdoor), rarely consider the role of vitamin D status. Glycaem ia and insulin secretion in elderly European men, however, relate to v itamin D status, independent of season or physical activity. Prolonged supplementation can improve glycaemia. Hypertension improves with vit amin D treatment with or without initial deficiency. Vitamin D status and climate are reviewed as risk factors for myocardial infarction; th e risk reducing with altitude despite increasing cold. Glycaemia and f ibrinogenaemia improve and insulin secretion increases in summer. Vari ation in vitamin D requirements could arise from genetic differences i n vitamin D processing since bone density can vary with vitamin D-rece ptor genotype. Vitamin D receptors are present in islet beta cells and we report insulin secretion in healthy Asians differing profoundly wi th the Apa I genotype, being independent of vitamin D status. Those at risk of vitamin D deficiency include the elderly, those living indoor s or having a covered-up style of dress, especially dark-skinned immig rants, and pregnant women, and these are groups recognized as being at increased risk of diabetes.