Revista Adolescência e Saúde

Revista Oficial do Núcleo de Estudos da Saúde do Adolescente / UERJ

NESA Publicação oficial
ISSN: 2177-5281 (Online)

Vol. 16 nº 2 - Apr/Jun - 2019

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Páginas 102 a 109


Evaluation of serum 25-hydroxy vitamin D levels in overweight adolescents

Evaluación de los niveles séricos de 25-hidroxi vitamina D en adolescentes con sobrepeso

Avaliaçao dos níveis séricos de 25-hidroxi-vitamina D em adolescentes com excesso de peso

Autores: Deisi Maria Vargas1; Fabrício Sbroglio Lando2; Maitê Fiegenbaum3; Nathalia Luiza Ferri Bonmann4; Clóvis Arlindo de Sousa5; Luciane Coutinho Azevedo6

1. Doctorate in Medicine and Surgery by the Universitat Autònoma de Barcelona (UAB - Spain). Teacher by the Health Sciences Center of the Regional Blumenau University Foundation (FURB). Blumenau, SC, Brazil
2. Mastering in Collective Health by the Regional Blumenau University Foundation (FURB). Blumenau, SC, Brazil
3. Resident in Pediatrics in the Santo Antônio Hospital. Blumenau, SC, Brazil
4. Graduating in Medicine by the Medicina College of the Regional Blumenau University Foundation (FURB). Blumenau, SC, Brazil
5. Doctorate in Sciences by the Public Health College of the Sao Paulo University (USP). Teacher of the Health Sciences Center of the Regional Blumenau University Foundation (FURB). Blumenau, SC, Brazil
6. Doctorate in Neuroscience by the Federal University of Santa Catarina (UFSC). Teacher by the Health Sciences Center of the Regional Blumenau University Foundation (FURB). Blumenau, SC, Brazil

Correspondência:
Deisi Maria Vargas
FURB - Campus 3, Sala A-302
Rua Sao Paulo, nº 2171. Itoupava Seca
Blumenau, SC, Brasil. CEP: 89030-001
(deisifurb@gmail.com)

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How to cite this article

Keywords: Vitamin D; Adolescent; Obesity; Overweight.
Palabra Clave: Vitamina D; Adolescente; Obesidad; Sobrepeso.
Descritores: Vitamina D; Adolescente; Obesidade; Sobrepeso.

Abstract:
OBJECTIVE: Evaluate the serum 25-hydroxy-vitamin D levels [25(OH)D] in adolescents with weight excess.
METHODS: Observational study with 86 adolescents with overweight followed during secondary healthcare service between August 2014 and August 2016. To diagnostic the overweight we used the World Health Organization criteria. The serum levels of 25(OH)D were categorized as: sufficiency (≥ 30 ng/mL), insufficiency (between 20 and 29 ng/mL) and deficiency (< 20 ng/mL). In some analysis, the deficiency and insufficiency categories of vitamin D were grouped into hypovitaminosis D category.
RESULTS: Only 38.4% of the adolescents had serum levels of vitamin D above the recommended level, 23.2% showed insufficiency, and 38.4% deficiency of vitamin D. There was a higher frequency of hypovitaminosis D (71.4% versus 52.3%, p = 0.03) and lower serum levels of 25 (OH) D (23.9 ± 8.7 ng / mL versus 28.1% ± 10.6, p <0.05) in adolescents with obesity in relation to overweight adolescents. There was no difference in 25(OH)D levels between sex and age groups.
CONCLUSIONS: Hypovitaminosis D occurred in 61% of adolescents and was positively associated to obesity. There was an inverse relationship between serum 25(OH)D levels and of weight excess degree.

Resumen:
OBJETIVO: Evaluar los niveles séricos de 25-hidroxi-vitamina D [25(OH)D] en adolescentes con exceso de peso.
MÉTODOS: Estudio observacional con 86 adolescentes con exceso de peso acompañados durante el servicio de atención secundaria entre agosto de 2014 y agosto de 2016. Para el diagnóstico de exceso de peso se consideraron los criterios de la Organización Mundial de Salud. Los niveles séricos de 25(OH)D fueron categorizados en: suficiencia (≥ 30 ng/mL), insuficiencia (entre 20 y 29 ng/mL) y deficiencia (< 20 ng/mL). Las categorías deficiencia e insuficiencia de vitamina D fueron agrupadas en la categoría hipovitaminosis D en algunos análisis.
RESULTADOS: Apenas 38,4% de los adolescentes tenían niveles de vitamina D arriba de lo recomendado, 23,2% tenían niveles  insuficientes y deficientes en 38,4%. Se observó mayor frecuencia de hipovitaminosis D (71,4% versus 52,3%; p = 0,03) y niveles séricos inferiores de 25(OH)D (23,9 ± 8,7 ng/mL versus 28,1 ± 10,6; p < 0,05) en los adolescentes con obesidad en relación a los adolescentes con sobrepeso. No hubo diferencia de los niveles de 25(OH)D entre las categorías de sexo y franja etaria.
CONCLUSIONES: La hipovitaminosis D ocurrió en 61% de los adolescentes y se asoció positivamente a la obesidad. Se observó relación inversa entre el nivel sérico de 25(OH)D y el grado de exceso de peso.

Resumo:
OBJETIVO: Avaliar os níveis séricos de 25-hidroxi-vitamina D [25(OH)D] em adolescentes com excesso de peso.
MÉTODOS: Estudo observacional com 86 adolescentes com excesso de peso acompanhados durante o serviço de atençao secundária entre agosto de 2014 a agosto de 2016. Para o diagnóstico de excesso de peso considerou-se os critérios da Organizaçao Mundial da Saúde. Os níveis séricos de 25(OH)D foram categorizados em: suficiência (≥ 30 ng/mL), insuficiência (entre 20 e 29 ng/mL) e deficiência (< 20 ng/mL). As categorias deficiência e insuficiência de vitamina D foram agrupadas na categoria hipovitaminose D em algumas análises.
RESULTADOS: Apenas 38,4% dos adolescentes tinham níveis de vitamina D acima do recomendado ,23,2% tinham níveis insuficientes e deficientes em 38,4%. Observou-se maior frequência de hipovitaminose D (71,4% versus 52,3%; p = 0,03) e níveis séricos inferiores de 25(OH)D (23,9 ± 8,7 ng/mL versus 28,1 ± 10,6; p < 0,05) nos adolescentes com obesidade em relaçao aos adolescentes com sobrepeso. Nao houve diferença dos níveis de 25(OH) D entre as categorias de sexo e faixa etária.
CONCLUSOES: A hipovitaminose D ocorreu em 61% dos adolescentes e associouse positivamente à obesidade. Observou-se relaçao inversa entre o nível sérico de 25(OH)D e o grau de excesso de peso.

INTRODUCTION

Vitamin D deficiency is reaching epidemic proportions worldwide and across all age groups. Current evidence suggests that there is a potential link between obesity and vitamin D deficiency in global populations.

Vitamin D is a prohormone with two major forms: ergocalciferol and cholecalciferol. Both are metabolized by the liver to produce 25-hydroxyvitamin D, which is later transformed by the kidney into 1,25-dihydroxyvitamin D, its active form. The bioactive form of vitamin D has numerous functions in the body and is involved in controlling gene expression in various cell and tissue types, regulating cell proliferation, differentiation and survival. Thus, the biological effects of vitamin D go beyond the regulation of mineral homeostasis and bone metabolism1.

In this context, the interest on the study of the association between serum vitamin D levels and metabolic diseases has gained prominence today, especially those related to obesity2. Hypovitaminosis D is common in many countries, regardless of nutritional status. In the pediatric age group, its magnitude seems to be higher in overweight children and adolescents and in those with chronic diseases3,4.


OBJECTIVE

The scarcity of national articles addressing hypovitaminosis D in overweight adolescents5,6 motivated this study. The objective of this study is to evaluate vitamin D levels in overweight adolescents, and their variations according to gender, age group and degree of overweight.


METHODS

The present study was observational, and was conducted with 86 overweight caucasian adolescents followed by the SUS secondary health care service, from August 2014 to August 2016. They were sequentially included in the study adolescents with the following characteristics: overweight, normal height for age (Z-score> -2), age-appropriate neuropsicomotor development and no vitamin D supplementation.

Study variables were gender, age, weight, height, BMI, degree of overweight and serum 25-hydroxy vitamin D [(25OH) D]. For the diagnosis of overweight we used the criteria recommended by the World Health Organization (WHO) that considers overweight a Z-score of BMI between +1 and <+2, obesity a Z-score between ≥ +2 and <+ 3 and severe obesity, ≥ +37. In the categorization of serum 25 (OH) D levels, the following cutoff points were used: sufficiency (values> 30 ng/mL); insufficiency (values between 20 and 29 ng/mL); and deficiency (values <20 ng/mL)8. Blood collection for biochemical analyzes occurred between spring and summer. The classification of hypovitaminosis D comprised the categories insufficiency and deficiency.

Statistical analysis was performed using the Kolmogorov-Smirnov test to evaluate the distribution of numerical variables in relation to normality. BMI, 25(OH) D and age presented parametric distribution and were expressed as mean and standard deviation of mean. To compare serum vitamin D levels between categories of sex, age and degree of excess weight, Student's t-test was used. Chi-square test was used to study associations between the frequency of hypovitaminosis D and the degrees of excess weight. The significance level adopted was p <0.05. The database was built using the EXCEL® program and statistical analyzes were performed using the StatPlus® program. The study was approved by the Human Ethics Committee of the Blumenau Hospital Foundation (opinion 2.090.278).


RESULTS

Between August 2014 and August 2016, 102 overweight adolescents were assisted at the secondary health care service. Of these, 86 (47 males) met the inclusion criteria. The description of the numerical and categorical data is shown in Table 1. The average age was 13.2 ± 2.1 years, and most of the studied adolescents were in the age group of 10-14 years and 51.2% had overweight. Six of the 42 adolescents in the obesity category had severe obesity.




The 25(OH)D value ranged from 11.5 to 50.1 ng/mL, with a mean of 26.1 ± 9.7 ng/mL. Most adolescents (61.6%) had serum 25 (OH) D levels below 30 ng / mL, and 38.4% were classified as deficient. There was no significant difference in 25 (OH) D levels between males and females (25.6 ± 9.9 versus 26.6 ± 9.5 respectively; p = 0.820) and between age groups (group 10 -14 years 25.9 ± 9.8 versus group 15 and 19 years 26.6 ± 9.8; p = 0.770). However, there was a difference in the mean values of 25(OH) D between overweight categories, with 25(OH) D lower in obese adolescents (Figure 1).


Figure 1. Mean values and standard deviation of Vitamin D according to the degree of excess weight (* Student's t-test).



The distribution of vitamin D status according to the degree of overweight is shown in figure 2. Hypovitaminosis D was more frequent in obese adolescents (Figure 2 - Panel A). When analyzing vitamin D status considering the three categories (sufficiency, insufficiency and deficiency), no significant difference was observed. However, vitamin D deficiency affected almost 50% of obese adolescents and 30% of overweight adolescents (Figure 2 - Panel B).


Figure 2. Distribution of Vitamin D status according to degree of overweight (* chi-square test; number of participants identified in bars).



DISCUSSION

The occurrence rates of hypovitaminosis D in overweight adolescents described in the international and national literature vary widely4,5,9-14. In the USA, 29% 9 and 43%10 of vitamin D deficiency and 79.8%10 of hypovitaminosis D are described in obese adolescents. In Ethiopia11, disability was found in 77.8% of overweight adolescents, while in Poland, disability was reported in 18 of 30 obese adolescents14. In Brazil, a study conducted in Juiz de Fora-Minas Gerais showed hypovitaminosis D in 68.8% of 83 overweight adolescents5, an occurrence similar to that found in this study. These studies have in common the inclusion of adolescents only and the geographical region.

Some of the risk factors for hypovitaminosis D described in the literature are: winter, short time outdoors, dark skin, older age, more advanced pubertal stage, obesity, low milk intake, low socioeconomic status, and female gender13,15. In this study, we found an association between the presence of obesity and hypovitaminosis D and found no association with females or older age. Williams10 and Vierucci16 also did not observe differences in vitamin D levels between genders. However, a national study conducted in Joao Pessoa-PB showed a higher occurrence of hypovitaminosis D in female adolescents6. Male adolescents tend to practice more outdoor activity with greater sun exposure and consequent higher vitamin D synthesis. On the other hand, female adolescents have a higher body fat rate17 and the frequency of sunscreen use by adolescents is generally higher in girls16. These are possible factors that would justify lower 25(OH) D in females.

We observed no difference in the occurrence of hypovitaminosis D between age groups. An American study showed an inverse association between age and hypovitaminosis D in obese adolescents with occurrences of 64% and 42% in the age group of 15-19 years and 10-14 years, respectively. Diet and lower sun exposure were considered the possible factors related to this difference10.

The Blumenau region has the world's third highest incidence of malignant melanoma18, which is a regional public health problem. Predisposing factors for the disease are: majority of the Caucasian population composed of German and Italian descendants, and ultraviolet radiation considered too high by the WHO. Thus, prevention actions are often performed18. This context could explain the absence of 25(OH)D values differences according to gender and age range, since the habit of protecting against skin cancer is present in most of the local population.

Obese adolescents seem to be more likely to have values below 25(OH) D. In this study, both hypovitaminosis D and vitamin D deficiency were more frequent in obese adolescents. This inverse association between the degree of overweight and serum 25(OH)D values was evidenced in other countries, although at different magnitudes4,12.

In addition to behavioral factors such as low precursor intake and reduced sun exposure19, hypovitaminosis D in overweight people may be related to intrinsic factors. Factors that may be involved in the pathophysiology of overweight-related hypovitaminosis D are: the presence of receptors in adipose tissue with vitamin D sequestration and reduced bioavailability to target tissues20, as well as increased serum leptin levels with inhibition of renal synthesis of the active form of vitamin D21.

Vitamin D has many functions in the body. The most traditionally known is its action on the skeleton. It is an essential micronutrient for bone health and plays a relevant role in the acquisition and maintenance of bone mass throughout vital cycles, being one of the protective factors against osteoporosis22. However, due to its extra-skeletal effects, hypovitaminosis D seems to be related to other types of chronic diseases, such as diabetes, dyslipidemia and asthma10. Thus, hypovitaminosis D could have a synergistic effect on the genesis of comorbidities associated with overweight such as hypertension, dyslipidemia and diabetes mellitus, leading to higher morbidity and mortality in this population23,24. The global consensus for the pediatric age group defines serum 25(OH) D levels above 20 ng/mL as vitamin D sufficiency. This cutoff level was defined considering their skeletal actions. However, there are recommendations for maintaining a serum vitamin D level ≥ 30 ng/mL for extra-skeletal actions8.

In terms of application in clinical practice, it is suggested that vitamin D status assessment be included in overweight adolescents, especially those with obesity. Maintaining a serum vitamin D above 30 ng/mL could be considered a treatment goal in this population group.

Limiting factors of this study are the low number of adolescents with severe obesity, making it impossible to analyze vitamin D levels in this category in relation to the other overweight categories; and the lack of information about conditions that may interfere with vitamin D synthesis, such as the use of sunscreen and the practice of outdoor activities.


CONCLUSIONS

Hypovitaminosis D affected a significant portion of the adolescents studied, and more than half of the obese adolescents had vitamin D levels below the recommended for extra-skeletal actions. There was no association between vitamin D levels and gender, as well as age group. There was an association between serum 25(OH)D and degree of overweight, with lower values in the group of obese adolescents.


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