The results from a nationwide paediatric study conducted as part of the CASPIAN-V programme in Iran have found that Vitamin D deficiency is associated with a higher prevalence of metabolic syndrome - a pre-cursor for non-communicable diseases (NCDs) in adulthood.
“An inverse association was observed between plasma vitamin D and the prevalence of metabolic syndrome,” wrote the researchers in the journal 'BMC Nutrition'.
In addition, low levels of plasma vitamin D were linked to a number of metabolic syndrome components. High fasting blood glucose, low high-density lipoprotein cholesterol, high triglycerides and abdominal obesity were more prevalent in the vitamin deficient group.
Metabolic syndrome is a clinical condition characterised by risk factors including dyslipidemia, elevated blood pressure, obesity and impaired glucose regulation. Evidence has suggested that vitamin D deficiency may increase the risk of NCDs associated with metabolic components. As vitamin D deficiency is more widespread among young people and NCDs often begin in childhood or young adulthood, it is particularly important to assess the link between vitamin D levels and cardio-metabolic risk factors.
No scientific consensus
However, there is conflicting evidence about the relationship between vitamin D deficiency and metabolic syndrome in children and adolescents. Some studies showed an inverse association while others did not reveal any association. In addition, few studies have investigated these associations in the Iranian pediatric population, where the prevalence of vitamin D deficiency, obesity and related metabolic disorders is high.
Therefore, the researchers conducted a nationwide cross-sectional study to examine the association between plasma vitamin D status and cardio-metabolic risk factors in a large, nationally representative sample of Iranian children and adolescents.
Independently funded by Alborz University of Medical Science, the study was performed as part of a programme called CASPIAN-V (Childhood and Adolescence Surveillance and Prevention of Adult Non-communicable disease). Participants were 2596 students (55% boys), aged between seven and 18 years.
All students completed a questionnaire, which included questions about consumption of vitamin D supplements, socio-economic status and leisure time activities. Measurements such as height, weight and waist circumference were taken along with blood samples for measuring serum concentration of 25-hydroxy vitamin D (25(OH)D.
More than 10% “vitamin deficient”
10.6% of students were found to be vitamin D deficient (defined as a serum 25(OH)D concentration of less than 10ng/ml), 60.5% were classed as having vitamin D insufficiency (serum 25(OH)D concentration of 10-30ng/ml) and 28.9% were considered vitamin sufficient (serum (OH)D level of more than 30ng/ml).
Prevalence of metabolic syndrome, high fasting blood glucose, low high-density lipoprotein cholesterol, high triglycerides and abdominal obesity was higher in the vitamin deficient group versus the vitamin insufficient and vitamin sufficient groups. Linear regression modelling showed that waist circumference, and high-density lipoprotein were “significantly associated” with vitamin D insufficiency. However, the results did not show any significant association between low serum vitamin D and blood pressure.
Whilst these findings add weight to the body of evidence in support of an association between vitamin D serum levels and metabolic syndrome, the researchers said additional research is essential to support a causal link.
“The biological mechanisms by which vitamin D may affect metabolic syndrome have not been completely clarified and are complex,” the researchers wrote.
Mechanisms still a mystery
What is known is that insufficient vitamin D serum can change metabolite function and impair cellular functions including endocrine pancreas, according to the researchers. They said vitamin D can status can also be associated with cardio-metabolic risk factors because of its immunomodulatory and anti-inflammatory properties. Additionally, studies have shown that vitamin D mediates down-regulation of the production of pro-inflammatory cytokines, stimulates insulin production and improves insulin sensitivity. And in another study, vitamin D insufficiency was found to increase C-reactive protein, which has been linked to an increased risk of CVD, obesity and metabolic syndrome.
“The mechanisms of association between vitamin D deficiency and metabolic syndrome in obese children should be elucidated in prospective studies,” advised the researchers.
They also recommended additional studies to determine whether low vitamin D serum levels in childhood affect the onset of CVD during adulthood.
Even with these knowledge gaps, they argued that there is a strong case for vitamin D supplementation in schools - especially in countries with a high prevalence of vitamin D deficiency - based on the available science.
Source: BMC Nutrition
Authors: Qorbani M, Heidari-Beni M, Ejtahed HS, Shafiee G, Goodarzi F, Saeed Tamehri Zadeh S, Khademian S, Mohammadian Khonsari N, Esmaeil Motlagh M, Asayesh H, Jabbari M, Heshmat R, Ebrahimi M, Kelishadi R
“Association of vitamin D status and cardio-metabolic risk factors in children and adolescents: the CASPIAN-V study”