Vitamin D status in young adults in Hong Kong : a biomarker approach to a public health concern

Abstract

Low vitamin D status is very common across the world, mostly due to the modern "indoor" lifestyle that leads to low exposure to sunshine. Low vitamin D status is clearly associated with bone disease, and there is accumulating evidence of links with various non-communicable diseases (NCDs), which are the leading causes of death and disability globally. However, the link between vitamin D deficiency and NCDs is not yet confirmed. It is noted that most NCDs become obvious in late adulthood, but the process of disease development begins at a much younger age. The underlying biological changes such as poor glycaemic control, poor lipid profile, inflammation, DNA damage, and oxidative stress, form a "common soil" for NCD development. If the link between vitamin D deficiency and the elements of the "common soil" is confirmed, public health strategies to improve vitamin D status are warranted. In Hong Kong, local studies indicate that vitamin D deficiency is highly prevalent, but data on young people are lacking. Therefore, this study aimed to determine the vitamin D status in a group of young, apparently healthy adults living in Hong Kong, and to investigate the inter-relationships between vitamin D status and the risk of NCD through a biomarker approach in a two-part study. In part 1 (the observational study), 196 (63 males and 133 females) young (18-26y), healthy, non-obese, non-smoking subjects were recruited with their written informed consent. Fasting venous blood and urine samples were collected from each subject. Plasma 25(OH)D concentration was measured as the indicator of vitamin D status, and a panel of sensitive biomarkers for glycaemic control, lipid profile, inflammation, DNA damage, and oxidative stress were measured. In part 2, a pilot supplementation trial was performed in a sub-group of those who were identified as being vitamin D deficient: 16 subjects received 2,400 IU vitamin D3/day for 12 weeks, while 11 received matching placebo. The improvement of vitamin D status and biomarker response were determined. The vitamin D status was found to be low: mean(SD) plasma 25(OH)D in the 196 subjects studied was 42(13) nmol/l, nearly all (194/196, 99%) had vitamin D insufficiency (defined as plasma 25(OH)D <75 nmol/l). Plasma 25(OH)D was found to be inversely associated with fasting plasma glucose and directly associated with the FRAP value ('total' and corrected for urate) for total antioxidant power (p<0.05). For those with plasma 25(OH)D <25 nmol/l (severe deficiency), significantly higher HbA1c, and total cholesterol/high density lipoprotein cholesterol ratio and lower high density lipoprotein cholesterol was seen (all p<0.05), in comparison with those with 25(OH)D≥25<50 nmol/l and those with 25(OH)D≥50 nmol/l. No significant association was seen between vitamin D status and DNA damage or any other biomarker. In the supplementation arm, correction of deficiency was linked to lower DNA damage (p<0.05), but no significant improvement was seen in any other biomarker. In addition, 146/196 of the subjects studied were found to have least one cardiometabolic disease related biomarker in the high risk category. In conclusion, this study provides new data on the vitamin D status of apparently healthy young adults in Hong Kong, and presents novel findings on the association between vitamin D status and well-established biomarkers related to NCD risk in this group. The high prevalence of low vitamin D status in our young people is an important public health concern in Hong Kong, as this may have long-term impact on their health, and results provide support for adoption of public health strategies to improve their vitamin D status through, for example education, food fortification schemes, and health screening programmes to identify vitamin D deficient individuals for appropriate supplementation.