Zinc deficiency in human nutrition

Zinc is needed to produce an active form of vitamin A, retinal, which is used in visual pigments. Zinc is also need by the retinol binding protein that transport vitamin A.

Zinc deficiency is uncommon in the United States and Canada, it usually occurs in people with illness that impair absorption.

Zinc deficiency can cause signs of vitamin A deficiency, even when there is sufficient vitamin A.

Zinc deficiency hinders digestion and absorption, causing diarrhea, which worsens malnutrition not only for zinc, but for all nutrients.

Zinc deficiency lowers immunity and infection causes zinc loss, more infection and more zinc loss.
Severe zinc deficiency is normally seen only in individual with genetic disorders. The clinical manifestation of severe deficiency in humans include slowing or cessation of growth and development, delayed sexual maturation and impotence, characteristic skin rashes, alopecia, chronic and sever diarrhea, immune system deficiency, impaired wound healing, diminished appetite, impaired taste sensation, night blindness, corneal changes and behavioral disturbances.
Mild zinc deficiency can impair weight gain and can prevent children from growing taller. It also increased susceptibility to life threatening infections in young children.

Human zinc deficiency first reported in the 1960s, in children and adolescent boys Egypt, Iran and Turkey.
Zinc deficiency in human nutrition