Madam
We read with great interest the article by Vijayakumar et al.(Reference Vijayakumar, Bhatia and George1), entitled ‘Vitamin D status of children in Kerala, southern India’, published recently in your journal. In this cross-sectional observation study, the authors studied the plasma vitamin D (25(OH)D) status of children in Kerala and its relationship with various social and demographic variables. We congratulate the authors for their excellent efforts; however, we want to add few additional points.
The sources of vitamin D in breast-feeding infants are breast milk and sunlight exposure. Human milk contains a relatively small amount of vitamin D that depends upon maternal vitamin D status(Reference Dawodu and Tsang2), so maternal serum vitamin D levels should have been assessed. The Indian Academy of Pediatrics has recommended vitamin D supplementation of 10 µg (400 IU) daily in infancy(Reference Khadilkar, Khadilkar and Chinnappa3). The authors(Reference Vijayakumar, Bhatia and George1) included relatively healthy children from 6 months to 12 years of age and they excluded children who received vitamin D supplementation. In the current scenario, nearly all breast-feeding infants receive oral supplementation and it would have been very difficult to get children less than 1 year old who had not received oral vitamin D supplementation.
The authors(Reference Vijayakumar, Bhatia and George1) divided the children into three subgroups (<5 years, 5–10 years and >10 years). All three groups had nearly similar vitamin D levels. Vitamin D levels are affected by sex, age, season, climate, BMI, place of living, ethnicity and pubertal status(Reference Sharawat and Dawman4). In our opinion, this study cohort probably had lower a number of infants and toddlers, who usually have infrequent sun exposure and their exposure to light is difficult to assess and monitor.
Subgroup 1 (<5 years) probably had highly skewed vitamin D levels, as the interquartile range was larger (39·6–70·9 nmol/l) for this group compared with the others(Reference Vijayakumar, Bhatia and George1). The Kruskal–Wallis test was used for non-parametric testing and it does not assume a normal distribution of variables. It would have been better to give the mean and sd of vitamin D levels for the different subgroups.
Vitamin D deficiency is pandemic and the estimated prevalence in northern India is 65–95 %(Reference Sharawat and Dawman4, Reference Sharawat, Sitaraman and Dawman5). Studies from the southern part of the country also showed a high prevalence. Harinarayan and colleagues(Reference Harinarayan, Ramalakshmi and Prasad6) studied vitamin D status in Tirupati, Andhra Pradesh. Their study included 1294 healthy participants (1148 adults and 146 children) and found that about 90 % of children in both rural and urban areas had deficient or insufficient vitamin D levels. Vijayakumar et al.’s(Reference Vijayakumar, Bhatia and George1) study showed only 11·1 % prevalence of vitamin D deficiency in relatively healthy children, which is completely different from the previous studies. Andhra Pradesh is also a coastal state and Tirupati is situated at latitude 13·4°N, longitude 79·2°E with nearly similar climate and food habits to Kerala’s. Further studies with a large sample size of children from different socio-economic backgrounds with proper dietary vitamin D intake can give the exact prevalence of vitamin D deficiency in the region.
Acknowledgements
Financial support: This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. Conflict of interest: None. Authorship: I.K.S. conducted the literature review, prepared the initial draft of the manuscript and gave final approval of the version to be published. L.D. critically reviewed the manuscript for important intellectual content and gave final approval of the version to be published. Ethics of human subject participation: Not applicable.
