Inadequate sunlight exposure due to excessive sunscreen use, extended indoor and limited outside activities; inadequate dietary intake (particularly vegans); body mass index (BMI); age and gender (elderly and multiple pregnancies in females); obese/overweight and malabsorption states (celiac disease, inflammatory bowel disease or liver cirrhosis); serum calcium and parathyroid hormone levels; and medication such as steroids are several other factors that may influence vitamin D status [29,73,74]. Here, PTH is linked to celiac disease.