Why are older adults more susceptible to infections

- including serious complications?

Older adults are more easily infected with influenza, COVID-19, and other infections and are also at greater risk that these infections will develop into complications such as pneumonia or acute respiratory distress syndrome (ARDS), which can be potentially life-threatening. One major reason is chronic “inflammaging” caused by widespread deficiencies of vitamin D, vitamin C, selenium, zinc, omega-3 fatty acids, and Q10. This not only increases the risk of infection but also the risk that the immune system will overreact with hyperinflammation, which is the real reason why respiratory infections and sepsis can become life-threatening. Overall, it appears that aging processes increase the need for specific nutrients, and if the immune system is well supplied, it will usually handle most pathogens without causing any symptoms.

Throughout life, the immune system’s task is to fight pathogens, and it is vital that all of its specialized units and defense forces function optimally. The innate immune system, which consists of various proteins (interferon, complement) and white blood cells (monocytes, macrophages, granulocytes, NK cells), eliminates most pathogens without us noticing anything at all. In the event of cell damage or actual infection, the innate immune system can also initiate inflammation. In this process, monocytes and macrophages act simultaneously as messengers that call in reinforcements from the adaptive immune system. The adaptive immune system develops after birth and consists of T cells, B cells, and antibodies.
During inflammatory processes, the immune system generates large amounts of free radicals as a kind of missile weaponry capable of destroying pathogens. It is important that these inflammatory processes proceed quickly and efficiently so the infection is completely suppressed, which often takes about a week. This should also lead to a form of immunization.
However, if the immune system does not function optimally, there is a risk of becoming infected. There is also a risk that the inflammatory processes will spiral out of control, resulting in hyperinflammation. This generates even more free radicals, increasing the risk of oxidative stress and chain reactions in which free radicals attack healthy tissue. When influenza or COVID-19 infections become life-threatening, it is precisely due to hyperinflammation, which can cause acute respiratory distress syndrome (ARDS) and other forms of organ failure that may be fatal. Hyperinflammation is also what makes sepsis life-threatening, making it one of the leading causes of death.
If the immune system functions poorly, there is also a risk that bacteria from the natural microflora of the throat will spread to the sinuses or lungs and cause secondary infections.

Oxidative stress and “inflammaging” are like a ticking time bomb

As part of the aging process, cellular energy metabolism and oxygen utilization become less efficient, leaving behind more free radicals as byproducts. Older adults’ often extensive medication use, chronic diseases, tobacco smoke, alcohol abuse, various toxic exposures, and other stress factors further increase the burden of free radicals.
With increasing age, the innate immune system becomes increasingly dysfunctional. This results partly in greater susceptibility to infections and partly in incorrect signaling by innate immune cells (monocytes and macrophages), leading to a chronic state of low-grade inflammation. This condition, known as “inflammaging,” increases the risk that the immune system will overreact with hyperinflammation when an infection occurs.
Although oxidative stress and inflammaging are not directly felt, the condition is like a ticking time bomb that can make infections complicated and, in the worst cases, life-threatening.

Oxidative stress and “inflammaging” are caused by nutrient deficiencies

As described, the immune system is highly specialized and requires a range of nutrients so that its various proteins and white blood cells can carry out their tasks quickly and efficiently. Broadly speaking, the immune system needs all vitamins and minerals to function optimally. However, older adults often lack vitamin D, vitamin C, selenium, zinc, omega-3 fatty acids, and Q10 for various reasons. Deficiencies in these nutrients make older adults (and everyone else) far more vulnerable, as outlined below.

Vitamin D

Vitamin D plays an important role in both the innate and adaptive immune systems on multiple fronts, including the production of antimicrobial peptides in the respiratory tract. In addition, vitamin D helps regulate inflammatory processes.
Summer sunlight is the primary source of vitamin D, which we produce in the skin from UVB radiation and a cholesterol precursor in our skin. However, the ability to produce vitamin D in the skin and activate it in the body declines with age. The dark winter months, darker skin pigmentation, overweight, diabetes, and the use of cholesterol-lowering statins all contribute to widespread deficiency.
The Danish Veterinary and Food Administration recommends that older adults take vitamin D supplements year-round (10-20 micrograms daily). However, there is no guarantee that this optimizes blood levels or immune function. Many leading researchers therefore argue that the actual daily requirement is between 50 and 100 micrograms.

Vitamin C

Vitamin C is essential for connective tissue and for the prevention and defense against infections. It is also important for the production of interferon, which prevents viruses from replicating in infected cells. The airways contain particularly large numbers of white blood cells that protect against airborne pathogens, and it is crucial that they are well supplied with vitamin C, especially when an infection is developing. In addition, vitamin C acts as a powerful antioxidant that counteracts oxidative stress and unwanted inflammation.
Most animals produce vitamin C themselves as needed and dramatically increase their own production during infections.
The recommended daily intake of vitamin C is 80 mg, but many older adults do not consume enough fruits and vegetables, which are good sources. Moreover, requirements increase with aging, oxidative stress, infections, smoking, use of heart medications, and other stress conditions.
While it is of course beneficial to obtain vitamin C from the diet, immune defenses can be further strengthened with larger, non-acidic supplements of 500-1,000 mg, and preferably more if an infection is developing.

Selenium

Selenium is incorporated into approximately 25-30 selenium-dependent proteins, and significant amounts are found in immune organs such as the thymus, lymph nodes, and spleen. Selenium is particularly important for immune communication, enabling the rapid production of millions of white blood cells and antibodies needed to protect against infections. Studies have shown that blood selenium levels drop sharply during infections to meet the immune system’s demands.
Selenium also helps prevent viruses from mutating, evading immune defenses, and becoming more dangerous - an effect that is particularly important in viral infections such as influenza, COVID-19, and herpes. In addition, selenium acts as a powerful antioxidant that counteracts oxidative stress and inappropriate inflammation.
Selenium deficiency is widespread throughout Europe, largely due to selenium-poor soil. Aging, oxidative stress, and infections further increase requirements. It has also been shown that statins inhibit the formation of an important selenium-containing antioxidant enzyme (GPX).
According to the new Nordic Nutrition Recommendations, the daily selenium intake is set at 75 micrograms for women and 90 micrograms for men. In many studies, 200 micrograms per day have been used, and intakes of up to 300 micrograms daily are considered safe.

Zinc

Zinc is involved in several hundred enzymatic processes and is important for both the innate and adaptive immune systems. Zinc is also required for cells to absorb and utilize vitamin D. In addition, zinc functions as an important antioxidant that counteracts oxidative stress and dysregulated inflammation. Good dietary sources include liver, meat, eggs, beans, and nuts, with zinc being most readily absorbed from animal sources.
The recommended daily intake of zinc is 10 mg. However, aging processes and acid-neutralizing medications impair absorption, increasing requirements. Needs also rise during infections, and daily intakes of up to 40 mg are considered safe.

Omega-3 fatty acids

The omega-3 fatty acids EPA and DHA are incorporated into cell membranes, where - together with omega-6 fatty acids - they regulate numerous biochemical processes, including inflammation. It is important to consume omega-3 and omega-6 fatty acids in the correct balance. However, modern diets often contain too little omega-3 from fatty fish and too much omega-6 from seed oils, dressings, mayonnaise, French fries, processed foods, and junk food. This increases the risk of inflammation.
Fatty fish and fish oil supplements contain EPA and DHA, which are the forms most readily utilized by the body.
In general, 1 gram of omega-3 per day is sufficient and can be obtained from a serving of herring or similar fish. During inflammation, however, 2-4 grams daily may be required, and it typically takes about a month for fish oil supplements to exert their full effect.

Q10

Q10 is a coenzyme that plays a crucial role in cellular energy production. It also functions as an important antioxidant that protects cells against oxidative stress.
In relation to the immune system, Q10 can be compared to the trigger of a firearm. It is essential for white blood cells to have the energy required to deploy their defenses.
Supplementation with Q10 can also reduce several markers of inflammation and oxidative stress.
The body produces most of its own Q10, but endogenous production declines with age, which many people notice after the age of 50 as their vitality is reduced. Statins and the osteoporosis drug alendronate are known to inhibit Q10 production.
Because declining Q10 production also impairs immune function, this can be compensated for with pharmaceutical-grade Q10 supplements. It should also be noted that selenium enhances the effect of Q10. Together, the two substances serve as natural anti-aging compounds that improve cardiovascular health.

• Acute inflammation is beneficial in infections and cell damage
• Chronic inflammation is harmful and tissue-destructive
• Many older adults suffer from chronic “inflammaging” and oxidative stress
• Aging processes, certain medications, and nutrient deficiencies contribute to increased vulnerability to infections and complications in older adults
• A strong immune system can usually fight pathogens effectively at any age

References:

Muhammet Mesut Nezir Engin, Öner Özdemir. Role of vitamin D in COVID-19 and other viral infections. World Journal of Virology. 2024

Runze Li et al. The Roles of vitamin C in infectious diseases: A comprehensive review. Nutrition 2025

Lutz Schomburg. The Immunomodulatory Effects of Selenium: A Journey from the Environment to the Human System. Nutrients 2024

Daryl Nault et al. Zinc for prevention and treatment of the common cold. The Cochrane Database of Systematic Reviews. 2024

Zhaoqi Yan et al. The relationship between dietary intake of ϖ-3 and ϖ-6 fatty acids and frailty risk in middle-aged and elderly individuals: a cross-sectional study from NHANES. Frontiers in Nutrition. 2024

Sara Dabbaghi Varnousfaderani et al. Alleviating effects of coenzyme Q10 supplements on biomarkers of inflammation and oxidative stress: results from an umbrella-meta analysis. Frontiers in Pharmacology. 2023