What Do Zinc Supplements Actually Do? A Scientific Evaluation From Colds to Immunity

Zinc supplements, frequently encountered on supermarket shelves and pharmacy displays, are promoted as a quick and easy solution for many health problems. Looking at the claims on the labels of these products, it is quite easy to think that an ordinary zinc pill works wonders in a wide range of areas, from the common cold to the immune system, and even male fertility. However, contrary to this popular belief, whether zinc supplements are the cure-all they are expected to be is a subject thoroughly researched by scientists. This mineral, which is essential for our body to maintain its basic functions, plays a critical role in hundreds of enzymatic processes, including metabolism, DNA synthesis, wound healing, and immune functions. Nevertheless, it should not be forgotten that since the body does not have a specialized system to store zinc, this mineral must be obtained regularly through food.

Zinc is naturally found in abundant amounts in meat, seafood (especially oysters), dairy products, legumes, nuts, and whole grains. It is known that individuals who eat meat and follow a balanced diet, especially in high-income countries, generally meet their daily zinc needs easily from the foods they eat. Despite this, it is stated that due to deficiencies in dietary habits, a risk of mild zinc deficiency is observed in three out of every ten people living in Australia. When zinc levels in the body drop, individuals become more susceptible to infections, and their recovery processes from illnesses are noticeably prolonged. Furthermore, even if it is not severe, the deficiency can lead to various adverse conditions such as hair loss, slowly healing wounds, changes in taste and smell, skin problems, and especially growth and development retardation in children.

Among the public, zinc is mostly known as a "cold fighter," and supplements are heavily marketed in this direction. However, in 2024, in the Cochrane review, which is considered the gold standard for evidence-based medical research, the results of 34 different studies examining the effects of zinc on the common cold were evaluated. Although 15 of the total 34 studies focused on preventing the common cold and 19 on treating it, the overall findings revealed that zinc supplements are not effective in preventing colds. Still, there are some findings indicating that zinc taken in lozenge or supplement form during the early stages of the illness may shorten the duration of the common cold by approximately two days compared to a placebo. On the other hand, whether it reduces the severity of the most tiring symptoms of the illness could not be fully clarified with the available data.

When it comes to the immune system, it has been scientifically proven that zinc supplements are beneficial only for individuals who are genuinely experiencing a zinc deficiency. Zinc, which helps immune cells develop, communicate with each other, and respond to infections, allows the system to function normally when present in sufficient amounts in the body. However, taking additional supplements for individuals with adequate zinc levels does not enhance immune functions beyond normal; on the contrary, excessive zinc intake can lead to serious problems such as immune suppression. A similar situation applies to male fertility; although zinc is necessary for sperm development and hormone regulation, its effects on fertility are exaggerated. In a large and comprehensive study involving over 2,000 couples, it was found that taking daily zinc and folic acid supplements for six months did not improve live birth rates or sperm quality compared to a placebo.

Experts emphasize that zinc supplements are not suitable for everyone and that the "more is better" logic, in particular, does not apply here. The recommended daily dietary zinc intake is about 8 milligrams for women and 14 milligrams for men, and these amounts can easily be obtained through a balanced diet. The safe upper limit for adults from all sources is around 40 milligrams per day; however, long-term high-dose intake can cause copper deficiency, anemia, nerve problems, and paradoxically, a weakened immune system by blocking copper absorption. Additionally, since zinc can reduce the absorption of certain medications, such as some antibiotics and blood pressure drugs, or disrupt the body's mineral balance, dosage and timing are extremely important for individuals taking medication. Therefore, instead of taking random zinc supplements to prevent colds, boost immunity, or increase fertility, the best approach is to consult a doctor, pharmacist, or dietitian first.