In a zinc deficiency, not all zinc functions decrease at the same rates. Some are impaired even in mild zinc deficiency, while others do not show a major impairment unless the deficiency becomes severe. Cell membrane functions may be the most sensitive change to a mild zinc deficiency. Still other zinc-requiring functions manage to use zinc so effectively that they operate fairly well even in a pronounced zinc deficiency. Thus, the symptoms of zinc deficiency depend a lot on its severity. The symptoms seem also to depend on what else is happening in the body at the same time, such that some zinc functions are affected mainly when zinc deficiency is combined with certain other factors (e.g., the presence of another disease or a period of rapid growth).
Linking poor health with zinc deficiency can be challenging. This is because zinc affects so many molecular processes and functions, either directly or indirectly. For example, severe zinc deficiency can affect bone growth. There are many possible reasons, including a number of zinc-dependent enzymes and hormones.
As noted at the beginning of the zinc section, severs deficiency in humans was first reported in areas of the Middle East. Symptoms included severely stunted growth, poor taste sensitivity, and impaired sexual maturation in the males.
In certain parts of the world, where economics limit food choices, the effects of zinc deficiency can be clearly seen in children. Symptoms include severe, even fatal diarrhea, poor growth, impaired vitamin A function, and high risk of pneumonia (presumably due to impaired immune function). In these same parts of the world, zinc deficiency in pregnant women may contribute to increased infant mortality and birth defects.
Besides dietary causes of severe zinc deficiency, this state can also be produced by a genetic condition where zinc absorption is impaired. This disease, acrodermatitis enteropathica, is recognizable by a skin condition that develops in infancy. The condition can be treated with supplemental zinc. Preterm infants can also show signs of zinc deficiency for the same general reason described for iron and preterm infants. However, the extent and significance of this state for zinc deficiency has not been well studied.
Marginal zinc deficiency may occur in many people, though there are still many questions to be answered. The classic example of documented marginal zinc deficiency involves a study done some time ago on a group of children in the Denver, Colorado area. The study reported that marginal zinc deficiency was responsible for impaired growth in a number of children. It is noteworthy that the marginal zinc deficiency seemed to be caused not by economic reasons, but rather due to poor food choices.
Many situations are suspected to produce marginal zinc deficiencies for various reasons. One reason can be moderately low intake, but other factors may include impaired zinc absorption, high zinc excretion, abnormal body distribution of zinc (e.g., one zinc protein absorbs high amounts of zinc), and high needs for certain zinc functions. However, in almost all of these situations, there is still uncertainty about how frequent the problem is and what symptoms result. One reason is that the symptoms may be produced by a combination of the zinc related problem plus some other factor. This makes it challenging to tease out how much zinc status is actually involved. Another major issue has been the lack of a good test for marginal in zinc defiency. Most of the tests that are used either are not sensitive to small changes in zinc status, have readings that can be affected by factors other than zinc status, require specialized equipment or expertise, or all of the above. Despite these barriers, zinc researchers are slowly making progress on marginal zinc deficiencies. A few examples of groups that may be prone to marginal zinc deficiencies are Crohn’s disease patients, people on kidney dialysis, diabetic individuals, older adults, sickle-cell anemia patients, alcoholics, and children with Down’s syndrome. Vegetarians may also be vulnerable to marginal zinc status. However, there is some contention that vegetarians adapt to low intake by reducing zinc excretion while increasing zinc absorption.
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