**2. Epidemiology**

Vitamin D deficiency is a major global public health problem in all aged groups, particularly in the Middle East. There is striking lack of data in infants, children and adolescents worldwide and in most countries of South America and Africa [9].

**97**

**Figure 2.**

*Vitamin D Metabolism (From Horlick [10]).*

*An Evidence-Based Review of Efficacy and Safety of Dietary, Natural Supplements…*

Of concern, even in countries where there is sun exposure all year-round, reports of deficiency is common in infants (90% in Turkey, 46% in black Americans, 96% in Kuwait and 99% in Indian), in children (58% in Belgium, 72% in Malaysia and 95% in Afghanistan), in adolescents (50% of non-whites in Canada, 46% in China and 45% in the United Arab Emirates) and in adults (52% of women in New Zealand,

Vitamin D is crucial in calcium and vitamin D metabolism, as its absence

1,25-Dihydroxyvitamin D interacts with the vitamin D receptor which increases

around 15% of dietary calcium and 60% of phosphorus is absorbed.

*DOI: http://dx.doi.org/10.5772/intechopen.89598*

97% in 62% in Korea and 77% in Brazil).

**3. Pathophysiology**

*An Evidence-Based Review of Efficacy and Safety of Dietary, Natural Supplements… DOI: http://dx.doi.org/10.5772/intechopen.89598*

Of concern, even in countries where there is sun exposure all year-round, reports of deficiency is common in infants (90% in Turkey, 46% in black Americans, 96% in Kuwait and 99% in Indian), in children (58% in Belgium, 72% in Malaysia and 95% in Afghanistan), in adolescents (50% of non-whites in Canada, 46% in China and 45% in the United Arab Emirates) and in adults (52% of women in New Zealand, 97% in 62% in Korea and 77% in Brazil).
