IPOVITAMINOSI D E FATTORI DI RISCHIO CARDIOVASCOLARI E METABOLICI NEI BAMBINI SOVRAPPESO E OBESI

Introduction. Hypovitaminosis D is an independent risk factor for cardiovascular morbidity. In adults, low levels of vitamin D are associated with hypertension, insulin resistance, cardiovascular disease, metabolic syndrome and diabetes. At present, no data are available about the relationship between cardiovascular and metabolic risk factors and hypovitaminosis D in children. Aim. The aim of this study was to evaluate the relationship between hypovitaminosis D and cardiovascular and metabolic risk factors such as hypertension evaluated with 24-h ABP patterns, hepatic steatosis, dyslipidemia and glucose intolerance in overweight and obese children and adolescent. Subjects and methods. Fifty-three Caucasian children (35 males and 18 females) aged 7-16 yrs were recruited among the overweight and obese children followed at the Department of Paediatrics of the Verona University Hospital, between October 2009 and July 2010. Exclusion criteria were chronic diseases, malformations, chronic use of drugs, including vitamin D or multivitamin supplements. We recorded anthropometric parameters, took blood samples for 25-hydroxivitamin D measurements, total LDL and HDL cholesterol, triacylglycerol, ALT and monitored ambulatory blood pressure (ABP). All children underwent OGTT and hepatic ultrasonography. Results. Hypovitaminosis D was diagnosed in 81% of the study group children (vitamin D deficiency (25(OH)D < 20 ng/ml) in 66% of children, vitamin D insufficiency (25(OH)D between 20 ng/ml and 30 ng/ml) in 15%). Vitamin D levels were negatively correlated with HOMAIR and fasting insulin, and positively with QUICKI. No relationship was found neither between fasting glucose, OGTT parameters and vitamin D levels, or between vitamin D total, LDL, HDL and cholesterol. We found nocturnal systolic pressure to be significantly higher in children with lower values of vitamin D. The 24-h diastolic BP load, the nighttime diastolic BP load and the nighttime systolic BP index increased progressively as the vitamin D deficiency worsened. We found a negative correlation between vitamin D levels and with 24-hour and nighttime systolic BP, 24-h diastolic BP load, nighttime systolic and diastolic BP load, 24-h systolic ABP index and nighttime systolic BP index. No relationship was found between daily diastolic hypertension level, daytime BP index or daytime BP load and vitamin D levels except for diastolic BP load. Conclusions. Our study is the first study that analyzed the relationship between vitamin D levels and 24-h BP patterns in obese children and adolescents; in agreement with previous studies it adds relevant information about the relationship between low vitamin D levels and high nocturnal blood pressure levels. Moreover we found a high prevalence of hypovitaminosis D in obese children and adolescent and a correlation between the severity of vitamin D deficiency and insulin resistance evaluated as HOMAIR. Prospective studies and vitamin D supplementation trials could confirm a cause-effect relationship between vitamin D and BP or insulin resistance also in children/adolescents.