Trace Elements // Zinc

Disease Risk Reduction

Delayed growth

Growth retardation and delays in weight gain in children are common symptoms of mild zinc deficiency.  

Especially in developing countries, many young children exhibit symptoms of zinc deficiency, a factor that inhibits growth. This was found in a meta-analysis of data from zinc intervention trials (15).

Studies show that zinc status affects cell-signaling systems controlling the body’s reaction to insulin-like growth factor-1 (IGF-1), the hormone that regulates growth (16). However, the exact mechanism responsible for the growth-limiting effects of zinc deficiency is not yet known.

Delayed brain development

A reduced capacity for attention in newborn babies and diminished motor function at six months of age has been linked to low zinc status in the mother during pregnancy. Supplementation with zinc has been shown to improve motor development in babies with a very low birth weight. It also promotes more energetic movement in babies and toddlers (17).

In first grade students in China, supplementation with zinc was also linked to improved ‘neuropsychological’ function, but this was only noted when other micronutrients were provided as well (18).

No link was observed between supplementation with zinc and improved brain function among children with growth retardation in two separate studies, however. 

More studies need to be carried out to assess the benefits of supplementation with zinc, even though some research indicates that zinc deficiency may delay cognitive development in young children (19).

Immune system dysfunction

For proper immune system function, zinc is essential (20). People with a zinc deficiency are therefore more prone to infectious diseases 21, 22).

Pneumonia

Risk of pneumonia may be positively affected by supplementation with zinc.  

Supplementation with zinc was shown to produce a significant reduction in the number of cases of pneumonia in children. This was observed during a pooled analysis of several studies from developing countries (27). In children under five, supplementation with zinc reduced the occurrence but not the duration of pneumonia or respiratory tract diseases, according to a meta-analysis (25)

Malaria

Supplementation with zinc may decrease the occurrence of malaria in children according to a few studies (28).

It was demonstrated in a randomized controlled trial in preschool children in Papua New Guinea that supplementation with zinc caused a 38% reduction in health center visits due to malaria (29). Furthermore, zinc supplementation may be of use in preventing more severe malaria cases. This was indicated by the reduction in the number of malaria cases accompanied by high levels of the malaria-causing parasite in the blood by 68%.

No effect on the frequency or severity of malaria cases however could be observed during a trial following over 700 West African children for six months (30). A further randomized controlled trial following over 42,000 children aged from one to 48 months demonstrated no significant reduction in deaths linked to malaria or other diseases through supplementation with zinc (31).

As yet, it is unclear whether supplementation zinc provides significant benefits for the treatment of malaria in children due to the conflicting nature of the data. 

Diarrhea

There is arguably a vicious circle when it comes to the relationship between zinc and diarrhea since chronic diarrhea contributes to zinc deficiency. The negative effects of zinc deficiency on the immune system are then likely to increase children’s susceptibility to infectious diarrhea. 

The duration and severity of acute and chronic diarrhea in children, as well as the survival rate, were demonstrated to be positively affected through zinc supplementation in combination with rehydration in a number of randomized controlled trials (23, 24). A meta-analysis of randomized controlled trials came to the conclusion that supplementation with zinc decreases the frequency, severity, and duration of cases of diarrhea in children under five (25).

Supplementation with zinc is advocated by the World Health Organization and the United Nations Children's Fund as part of the treatment of diarrhea in young children (26).

Immune response in the elderly

That the elderly are more prone to mild zinc deficiency has been linked to age-related deterioration of the immune system. Zinc supplementation trials have however as yet produced only mixed results relating to immune response. 

Zinc supplementation has been found to positively affect some aspects of the immune response in people over 65 in randomized controlled trials (32, 33).

According to other studies, supplementation with zinc shows no improvement regarding immune function. Further research is therefore required before any firm conclusions can be drawn concerning immune response in elderly people. 

Complications in pregnancy

Low birth weight, premature birth, complications relating to labor and delivery, and abnormalities in developing fetuses have all been linked to insufficient zinc intake among expectant mothers (34).

American trials and trials in developing countries relating to zinc supplementation have however been unable to produce conclusive results (17).

Zinc supplementation of expectant mothers has been found to increase birth weight and reduce the probability of premature birth in some studies but two randomized controlled studies following Bangladeshi and Peruvian women maintained that supplementation with zinc had no effect on low birth weight or premature birth frequency (35, 36).

No conclusive results have been provided by studies designed to record how supplementation with zinc affects labor and delivery complications. However, not many of these have been carried out in populations considered to be zinc-deficient (17).

Supplementation with zinc during pregnancy has been linked to a 14% reduction in premature births, according to a review of 17 randomized controlled trials. Low-income women were the ones that mainly exhibited the lower occurrence of premature births (37).

Zinc and Depression:

Results: Seventeen studies, measuring peripheral blood zinc concentrations in 1643 depressed and 804 control subjects, were included in the Meta-Analysis.

- Zinc concentrations were approximately −1.85 mmol/L lower in depressed subjects than control subjects. 

- Greater depression severity was associated with greater relative zinc deficiency. (72)

Zinc, Ageing and Alzheimer’s Disease:

We examined the distribution of zinc in the periphery (erythrocytes and serum) in a large, well characterised cohort, the Australian Imaging, Biomarkers and Lifestyle (AIBL) study, in order to determine if there is systemic perturbation in zinc homeostasis in Alzheimer’s disease (AD). 

Results: We observed an age dependent decrease in serum zinc of approximately 0.4% per year. When correcting for the age dependent decline in serum zinc no significant difference between healthy controls (HC), mildly cognitively impaired (MCI) or AD subjects was observed. (71)

Zinc and Alcoholic Liver Disease (ALD):

There is major zinc dyshomeostasis with ALD. This is mediated, in part, by poor intake and absorption, increased excretion, and altered zinc transporters, especially ZIP14. Zinc deficiency plays an etiologic role in multiple mechanisms of ALD, ranging from intestinal barrier dysfunction to apoptosis.

Results: Zinc supplementation is highly effective at correcting these ALD mechanisms and preventing/treating experimental ALD. (70)

Zinc and embryogenesis:

A large percentage of preterm neonates is affected by mild to moderate subclinical zinc deficiency. Maternal zinc restriction during pregnancy influences fetal growth, while adequate zinc supplementation during pregnancy may result in a reduction of the risk of preterm birth. (73)

Zinc and Cancer:

Meta-analysis results: Comparing the highest with lowest categories, higher zinc intake was significantly associated with reduced colorectal cancer risk (69).

Zinc and pneumonia:

Pneumonia is a major cause of morbidity and mortality of children. Zinc is known to play a central role in the immune system. The deficiency of zinc increased susceptibility to infectious diseases.

Results:  Zinc given as an adjunct to the treatment of severe pneumonia is effective in reducing the mortality of severe pneumonia, and has no significant effects on treatment failure and change of antibiotic therapy. (74)

Results: We included six studies that involved 5193 participants. Analysis showed that zinc supplementation reduced the incidence of pneumonia by 13% and prevalence of pneumonia by 41%. (68)

Zinc and fertility:

Meta-analysis results: Folate plus zinc supplementation has a positive effect on sperm characteristics in sub fertile men. However, these results should be interpreted with caution due to the important heterogeneity of the studies included in this meta-analysis. (66)

Meta-analysis: The present study showed that the zinc level in the seminal plasma of infertile males was significantly lower than that of normal males. Zinc supplementation could significantly increase the sperm quality of infertile males. (75)

Zinc and acute diarrhea in children:

Pooling Chinese and non-Chinese studies yielded an overall 26% reduction in the estimated relative risk of diarrhea lasting beyond three days among zinc-treated children. Studies conducted in and outside China report reductions in morbidity as a result of oral therapeutic zinc supplementation for acute diarrhea among children under five years of age. The WHO recommendation for zinc treatment of diarrhea episodes should be supported in all low- and middle-income countries. (67)

 

Authored by Dr Peter Engel in 2010, reviewed by Giorgio La Fata on 29.09.2017