Key nutrient shortfalls may increase the risk of infections
Ideally, a well-balanced, nutrient-dense diet, including a variety of colorful fruits and vegetables, whole grains, legumes, healthy fats, and a balanced selection of proteins can meet all of one’s daily requirements for essential vitamins and minerals, as well as essential fatty acids (EFAs), amino acids, and other nutrients.
In practice, however, this is a tall order. It is difficult for many of us to obtain a sufficient variety and/or quantity of wholesome foods to fulfill all of our nutritional needs on a regular basis, and there is often a gap between what we consume and what we require. In addition to compromising overall health, inadequacies in key nutrients can impair immune function.
A recent article (which we’ll refer to as the 2020 study), published in the peer-reviewed scientific journal Nutrients, highlights the magnitude of the problem. The authors carried out an analysis of usual micronutrient intakes based on data from the National Health and Nutrition Examination Surveys (NHANES), a nationwide survey conducted by Centers for Disease Prevention and Control (CDC).
Using data obtained between 2005 and 2016, the authors compared the usual dietary intakes from food and supplements to the estimated average requirement (EAR) for a particular nutrient, with a focus on nutrients of importance for immune function. In addition to looking at nutrient intakes from food only, they also examined the effects of supplementation.
The results revealed substantial inadequacies in vitamins A, C, D, and E, as well as zinc, across the population, especially among individuals who relied on food alone to meet their nutrient needs. Insufficient intakes of these nutrients in particular significantly compromises immune function, as we’ll discuss today.
Vitamin D insufficiency has a significant impact on immune health. The 2020 study adds to the concern, showing that 95% percent of non-supplemented adults had vitamin D intakes below the EAR.
Vitamin D is known as the sunshine vitamin because it is generated within the skin upon exposure to ultraviolet B (UVB) rays, the rays responsible for suntans., Vitamin D status tends to be at its lowest in winter,, coinciding with the seasonal prevalence of respiratory infections. During the 1918–1919 “Spanish flu” pandemic, for example, greater fatality rates occurred in those with less sunlight exposure.
Insufficient vitamin D intakes are strongly associated with an increased risk of respiratory infections, including influenza and pneumonia, and with an increased severity of these infections.,, Further studies have shown that supplementation with vitamin D may cut the risk of acute respiratory tract infections by an average of one-third or more, and that individuals with low starting levels of 25(OH)D (<40 nmol/L) are likely to see the most benefit., A 2017 systematic review concluded that vitamin D supplementation could help protect against acute respiratory tract infections overall.
Vitamin E, the main lipid-soluble antioxidant in the body, prevents oxidative damage to membrane polyunsaturated fatty acids, and thereby preserves the function of immune cells. The 2020 study showed that 84% percent of non-supplemented adults had vitamin E intakes below the EAR.
Vitamin E deficiency impairs both humoral and cell-mediated immune functions.,, A deficiency of this vitamin can increase the risk of infections, and exacerbate the damage that occurs once an infection takes hold., Vitamin E supplementation has been shown to improve measures of immune function and to reduce the incidence and severity of respiratory infections in the elderly, whose immune systems may be compromised due to age.,,,
Vitamin C (ascorbic acid) is a water-soluble antioxidant that is indispensable for a healthy immune response against viral and bacterial infections.,,,,, The 2020 study showed that 46% of non-supplemented adults had vitamin C intakes below the EAR.
Multiple clinical trials have shown that vitamin C supplementation may shorten the duration and severity of common cold symptoms, and also reduce the incidence of colds in individuals with suboptimal vitamin C levels. A meta-analysis showed that extra doses of vitamin C could benefit patients who contract the common cold, even if they were already supplementing vitamin C regularly. More vitamin C is consumed by the cells of the body in the course of fighting infections, so relatively high doses are needed to influence the course of respiratory infections once they have taken hold.,,,,
Adequate vitamin A has long been associated with resistance to infections., This vitamin plays a critical role in the differentiation, maturation, and function of immune cells, both for innate and adaptive immunity,,,, and it can even favorably modulate the gut microbiota.
The 2020 study showed that 45% of non-supplemented adults had vitamin A intakes below the EAR. Vitamin A deficiency has been observed to increase the risk for viral infections, in both children and adults.,, Acute illnesses and infections may also deplete serum retinol concentrations and increase the requirements for this vitamin.,, Vitamin A deficiency can also impair the efficacy of vaccinations by reducing antibody responses.
Zinc supports innate and acquired immunity through direct, indirect, and antioxidant mechanisms.,,, The 2020 study showed that 15% of non-supplemented adults had zinc intakes below the EAR. Additional studies have shown that the prevalence of marginal zinc intakes depends on age, ranging from 12% of younger adults to 30% or more of individuals over the age of 60.,,
Even mild zinc deficiencies can increase the risk and severity of viral infections, including respiratory infections such as influenza and pneumonia.,,, To illustrate the importance of zinc, an investigation of the nutritional status of patients admitted to a hospital’s infectious disease ward revealed that two thirds of the patients were deficient in zinc. Zinc deficiency not only compromises immunity, but also shifts the immune system toward an inflammatory state that can predispose the body for damage to the lungs and other organs., Conversely, supplemental zinc may help reduce the risk of infections.,,
A significant number of Americans did not meet estimated average requirements for vitamins A, C, D, and E, and zinc.
The immune system needs multiple micronutrients, including vitamins A, D, C, E, B vitamins (folate, vitamin B6, and B12), zinc, iron, copper, and selenium, which play vital, often synergistic roles at every stage of the immune response.,
The 2020 study shows that a significant number of Americans did not meet estimated average requirements for vitamins A, C, D, and E, and zinc. Selenium was not identified as having a high prevalence of inadequacy, but a study of infectious disease patients found that 47% were deficient in selenium.
The 2020 study further showed that the consumption of dietary supplements reduced the prevalence of nutrient inadequacies, although some adults taking supplements were still not meeting the EARs.
In sum, data strongly suggests we should assess whether our diets (and supplements) are providing adequate intakes of key immune health nutrients, and adjust our intakes accordingly.
For more information on the micronutrients discussed in this article, please see these additional NutritionInFocus articles:Click here to see References
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