Zinc plays a central role in the functioning of our immune system. It was recognized decades ago that a lack of zinc can negatively affect the function of several immune cells and aggravate inflammatory processes. (1,2) Not only do some immune cells not function properly, but their ratio and thus the balance of the immune system is disrupted. As a result, the body is less able to suppress inflammatory processes and increasingly loses control. Such chaos is very conducive to the development of infections. (2,3) 

People with a zinc deficiency are much more likely to get infections of various kinds, and the course of these infections is more severe. For example, children with inadequate zinc intake are nearly twice as likely to get diarrhea and 3.5 times as likely to suffer from lower respiratory tract infections. (4) Further studies on children living in poverty and eating a deficient diet have also found that zinc supplementation significantly improved their immunity and growth. (5,6)   

Supplementation with zinc in the form of nutritional supplements has led to mixed but mostly positive results, demonstrating that if someone already has a good supply of zinc, it is less important to take it additionally during infections. For colds, it may be useful for a few days, but it is not recommended to take more than 100 mg, as there is no additional benefit at higher doses. At such high levels, however, it can cause problems such as copper deficiency. 

What's certain is that zinc, like higher doses of vitamin C, can shorten the duration of colds by several days when used in an orally soluble form. These became popular after a researcher's daughter was cured within hours after letting a zinc capsule dissolve in her mouth instead of swallowing it.  

The mixed results of zinc supplementation can also be explained by the fact that different studies used different doses and forms of zinc, and that the preparations contained different excipients that may have inhibited the zinc from having an impact. Let's take a closer look at how zinc was tested and what the results were! 

Zinc’s effect on the common cold 

The effects of zinc supplementation on the common cold have been tested in several randomized trials, the pooled results of which have been the subject of several meta-analyses. The point of a meta-analysis is that more accurate conclusions are possible from the results of several high-quality studies than from a single study alone.  

The first was published in 2012, which included 17 randomized trials with a total of more than 2000 participants. (7) Zinc supplementation significantly shortened the duration of colds, by an average of two and a half days in adults and by much less in children. Supplementation led to highly variable results in different studies and individuals, suggesting that the available zinc supply at the start of the study had a major impact on the effectiveness of therapy. Of the different forms of zinc, zinc acetate was the best, although no significant differences were found between them. Mild nausea and a lingering unpleasant taste were common side effects.  

In 2017, another meta-analysis came to similar conclusions. Here, 7 trials were selected that used zinc supplementation in doses over 75 mg, in the form of zinc acetate or zinc gluconate. (8) These reduced the duration of colds by an average of 33%, but supplementation with zinc acetate was more effective, yielding a 40% reduction. Another important finding of the meta-analysis is that doses exceeding 100 mg are hardly more effective than supplementation between 75-100 mg, so if the goal is to reduce the duration of a cold with zinc supplementation, it is not worth exceeding this amount. If aiming to recover from a cold, it is also worthwhile to increase vitamin C intake, which will help shorten the duration of the illness. (9) 

Summary 

Zinc plays a central role in immunity and it is recommended to consume at least 15 mg per day to prevent zinc deficiency. During colds or other infections, an additional supplement of 75-100 mg in the form of orally soluble zinc acetate can be effective. It is important to note that this level of zinc consumption is unsafe in the long term and can cause copper deficiency and other serious problems, so only employ these amounts for a few days.