The goal of this observational study is to verify the role of adipose tissue in determining the vitamin D serum level after monthly oral administration in subjects with vitamin D deficiency.

The main questions it aims to answer are:

• Adipose tissue represents a storage environment for vitamin D or it's an environment where vitamin D is sequestered and no longer released
• On the other hands, it's possible to verify whether the adipose tissue carries out a bi-modal activity towards vitamin D
• If adipose tissue exerts a bi-modal effect, it is possible to identify a specific threshold between the two effects Participants will undergo anthropometric measurements (height, weight, waist/hip ratio waist circumference) at baseline and after 6 months of intake of cholecalciferol 50,000 IU/month

Vitamin D deficiency and insufficiency are prevalent worldwide, and various factors contribute to their occurrence, including low sun exposure, poor dietary intake, obesity, and abdominal obesity. Abdominal obesity, assessed by waist circumference (WC), is associated with metabolic syndrome and has been linked to low vitamin D levels. This study aimed to investigate the relationship between visceral adipose tissue (VAT) and vitamin D levels, particularly examining the potential threshold for vitamin D storage and sequestration by adipose tissue.

The study is conducted on patients with hypovitaminosis D in an internal medicine outpatient department. Blood samples for the evaluation of calcium and vitamin D levels are collected at baseline and after six months of monthly cholecalciferol supplementation. Ultrasonography are used to evaluate adipose tissue measurements, including subcutaneous adipose tissue thickness, VAT, preperitoneal adipose tissue (PPAT), and prerenal adipose tissue (PRAT). Anthropometric measures such as waist-to-hip ratio and waist-to-height ratio are also assessed.

Inclusion Criteria:

• Vitamin D level < 20 ng/ml
• BMI > 24

Exclusion Criteria:

• Administration of vitamin D metabolites in the last year
• Previous diagnosis of metabolic bone diseases
• Previous diagnosis of endocrine diseases
• Previous diagnosis of cancer

Patients referred to the internal medicine clinic for cardiovascular evaluation.