Elsevier

Public Health

Volume 152, November 2017, Pages 75-78
Public Health

Short Communication
Sedentary behavior is associated with lower serum concentrations of vitamin D in Brazilian children

https://doi.org/10.1016/j.puhe.2017.07.021Get rights and content

Highlights

  • It was found a high prevalence of inadequate serum vitamin D in children, even in the case of a tropical country.

  • Vitamin D intake was below the recommendation, thus underscoring the importance of encouraging children to eat source foods.

  • Modifiable behavioral factors associated with lower serum vitamin D were the highest screen time and less sun exposure.

  • Darker skin color and winter also contributed to reduce serum concentrations of vitamin D.

Introduction

Vitamin D is treated as a hormone responsible for the homeostasis of calcium and phosphorus, contributing to adequate bone formation.1 Currently, vitamin D deficiency has been considered as a worldwide public health problem and is related to decreased dietary calcium absorption directly influencing bone mineralization and, more recently, to extraskeletal diseases such as some types of cancer, type 2 diabetes mellitus, autoimmune diseases, metabolic syndrome, hypertension, and infectious diseases.1, 2

The major source of vitamin D is the endogenous cutaneous synthesis from sunlight, around 90%, but it can also be obtained from dietary sources such as cod liver oil and fatty fish (salmon, tuna, sardines, mackerel), fortified foods, and in small quantity in milk and eggs.2

In countries located between the tropics, such as Brazil, where there is a greater incidence of sunlight, a lower prevalence of hypovitaminosis D is expected. However, studies have found a high prevalence of vitamin D insufficiency in the Brazilian population.3

Developed and developing countries are currently facing an unrecognized and untreated public health problem of vitamin D deficiency.4, 5 Several studies have reported a high prevalence of vitamin D deficiency in healthy children associated with the lowest socio-economic status, younger age group, female sex, limited sunshine exposure, and no vitamin D supplementation; on the other hand, opposite results found no relationship between vitamin D and sex, sunshine exposure, or nutritional status.5, 6, 7 Studies assessing the serum concentration of vitamin D in prepubertal children and its relationship with behavioral and sociodemographic factors are scarce in Brazil. In view of its potential impact on children's growth and adverse health conditions, it is important to identify modifiable risk factors associated with this deficiency in order to promote greater surveillance of professionals in prevention and treatment. Given the above, this study aimed to assess serum concentrations of vitamin D and behavioral and sociodemographic factors associated in Brazilian prepubertal children. This would enable the identification of barriers to guide future campaigns for the prevention of hypovitaminosis D.

Participants in this study were from the Educational Health Assessment Research, a representative study, with children aged between 8 and 9 years enrolled in urban schools in Viçosa, Minas Gerais, Brazil. In 2015, the city had 24 urban schools (17 public and 7 private) that served children aged between 8 and 9 years old, totaling 1464 children. The sample calculation was performed using the software Epi Info 7.2.1 considering the analysis of multiple outcomes with prevalence of 50%, tolerated error of 5%, 95% of confidence interval, significance level of 5%, and estimated loss and confunder factors of 20%, resulting in the calculation of 366 children. Children were included by random selection. This study was approved by the Ethics Committee on Human Research of the Federal University of Viçosa (protocol number 663171/2014).

A semistructured questionnaire was applied to parents or guardians to assess the socio-economic and demographic variables such as sex, skin color, maternal education, total and per capita income.

Based on the child's life habits, physical exercise was considered as regular physical activity when outside of school and at least once a week and sedentary behavior was defined as activities that do not increase energy expenditure substantially above rest, such as sitting, watching television, or engaging in other forms of screen-based entertainment.8

With the help of the parents, the average time of daily sun exposure was assessed including outdoor leisure time and walking in the sun in addition to the habit of using sunscreen by children.

Dietary intake was assessed by three 24-hour recalls, obtained in non-consecutive days with one on the weekend, which were quantified in software Diet Pro 5i.

Measurement of calcidiol [25(OH)D] (Architect®) and parathyroid hormone (Access® Intact) was performed by chemiluminescence. 25(OH)D was determined by the Architect® 25-OH vitamin D assay which was developed to have correlation coefficient ≥0.80 for serum samples when compared with LIAISON® DiaSorin 25-OH vitamin D total assay. The Architect 25-OH vitamin D assay has been developed to have an imprecision of ≤10% within laboratory total CV. Serum vitamin D levels were classified as deficient calcidiol (<20 ng/mL), insufficiency (20–29 ng/mL), and sufficiency (≥30 ng/mL).9

Multiple linear regression analysis was performed to assess the effect of independent variables in serum concentration of vitamin D. The criteria defined for the inclusion of variables in multiple linear regression was the association with the dependent variable in simple linear regression analysis, considering a value of P < 0.20. The final model was adjusted by intake of vitamin D, sex, and parathyroid hormone.

Section snippets

Factors associated with vitamin D concentration

More than half of the Brazilian children had insufficiency/deficiency of vitamin D (56.3%). The mean serum concentration of vitamin D in children was classified as insufficient (29.3 ng/mL), with 12.8% deficient and 43.5% insufficient. The prevalence of insufficiency/deficiency was 52.2% in boys and 62.2% in girls (P = 0.05).

The boys had a higher frequency of regular physical activity (P = 0.011) and screen time higher than 2 hours/day (P = 0.026). Girls had higher frequency of low sun exposure

Acknowledgments

The authors are grateful to the National Council for Scientific and Technological Development (CNPq) for financial support (grant number 478910/2013-4) and to Coordination for the Improvement of Higher Education Personnel (CAPES) for the granting of a master's scholarship.

Ethical approval

This study was approved by the Ethics Committee on Human Research of the Federal University of Viçosa (protocol number 663171/2014).

Funding

This work was supported by National Council for Scientific and Technological Development

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