Background: Zinc is vital to many physiological and biological functions in the human body. It is essential to many structural, catalytic and regulatory functions including the formation and stabilisation of insulin complexes. In addition to the link between zinc and insulin, having optimum zinc status can contribute to well-controlled diabetes. The main effect of type 2 diabetes mellitus (T2DM) on zinc homeostasis is hypozincaemia, primarily due to hyperzincuria and to lesser extent decreased gastrointestinal reabsorption of zinc. However, the results on this are often contradictory displaying the need for more uniform analysis of the effects T2DM has on zinc status.
Objective: The aim of this project was to conduct a systematic review of cross sectional studies, comparing the zinc status of those with T2DM to a healthy population.
Methods: This systematic review follows the Cochrane design for systematic reviews. Data sources were English language studies in Ovid MEDLINE (R) 1946 to February 2016, Ovid Embase Classic + Embase 1947 to February 2016, SCOPUS and Web of Science core, with manual searches of in-text citations. Criteria for eligibility of studies included: studies must be cross-sectional investigating zinc status of subjects over the age of 18 years with T2DM in comparison to healthy subjects. Studies must include measures of serum/plasma or blood glucose, HbA1c or a combination and data on zinc status biomarkers (serum, plasma, hair, urine, nails, erythrocytes, zinc-related enzymes and dietary zinc).
Results: From the 13,258 studies identified, 29 of these met the eligibility criteria for the current systematic review. These studies came from 16 countries including; England, Pakistan, Iran, China, Nigeria, Turkey, Ghana, Egypt, Israel, Slovakia, Ireland, the USA, India, Austria, Bangladesh and Saudi Arabia. The majority of the studies measured zinc status through serum or plasma, followed by hair zinc and urinary zinc, with the remaining six studies measuring a combination of the afore mentioned biomarkers with the addition of erythrocyte zinc. Of the 26 studies that measured serum/plasma zinc, 21 concluded that those suffering from T2DM have lower zinc status than a healthy population and 17 stated that their results were significant (p<0.05). All studies that measured hair or erythrocyte zinc as a biomarker of zinc status showed that it was lower in those with T2DM. All of the remaining studies that measured urinary zinc status stated that it was higher in those with T2DM. We found a positive correlation with absolute HbA1c and serum/plasma zinc levels, p= 0.002.
Conclusion: This systematic review concludes that those with T2DM generally have a lower zinc status than the healthy population. Our study has highlighted that plasma, serum, hair, and erythrocyte zinc biomarkers are generally lower and urinary zinc is higher among those with T2DM, when compared to a healthy population. The central view throughout this review is that those suffering from T2DM are prone to hyperzincuria, which can distort the homeostasis of zinc in the body.
