At The Cold Front

It’s that time of year when we need few reminders that we live in a microbial world. If there’s any consolation to the advent of cold and flu season compounding the COVID-19 pandemic, it’s that it caps two years of intense focus on ways to fortify immune defenses against respiratory viruses.

Research indicates that 15 percent of common colds are, like COVID-19, caused by a coronavirus. While cold-causing coronaviruses are as transmissible as COVID-19, they favor the upper respiratory tract rather than settling deep into the lungs. The damage they inflict tends to be short-lived.

On the other hand, as they continuously circulate around the globe, along with 200 other respiratory bugs, coronaviruses have a proclivity to reinfect their victims. Like all infections, they elicit an immune response that quickly produces inflammation, which, in its rush to kill off invaders, pours toxic substances into systemic circulation. Much as it is part of immune defense, inflammation is ultimately a destructive process, a known disruptor of mental function and implicated in every mental illness.

The first and fastest players to reach the site of infection are constituents of the innate immune system—so-called because it is just there, waiting to pounce on any pathogen. It makes staying immunologically fit an imperative.

Immune fitness owes something to physical fitness, and the same lifestyle factors contribute to both. Regular physical activity maintains immunity. So does a healthy diet, especially one that feeds the gut microbiome plenty of fiber and plant matter.

A number of specific micronutrients play significant roles, too. Vitamins C and D and the mineral zinc are chief among them. Multiple studies have found that each of these contributes to immune function in a number of specific and nonspecific ways. What is more, deficiencies of these micronutrients consistently show up among those who wind up infected.

Vitamin C has long been known as an infection fighter. An antioxidant, it not only fortifies the mucosal barrier against invasion but also beefs up the killing capacity of neutrophils and other innate immune cells rushing to the scene. It is a hustler, as well, in the second wave of immune defense—the adaptive, or acquired, response—involving the production of B and T cells targeting specific antigens. These are the troops that create immune memory for invading pathogens in the future.

Although vitamin C is an essential micronutrient, 46 percent of American adults have inadequate intake, according to the National Health and Nutrition Examination Survey (NHANES). Not only does vitamin C deficiency increase susceptibility to infection, infections, in turn, make significant demands on vitamin C levels.

Maintaining adequate tissue levels of vitamin C to ward off infection is one thing, and studies show that regular vitamin C supplementation can prevent respiratory and other infections. Fighting off active infection is another matter, compounding the case for fortification.

Vitamin D, created when sun strikes the skin, is a nutrient with an ever-expanding portfolio, involved in many systems of the body, including the brain. Its significance to the immune system is still not fully known, but almost every cell in the immune brigade has receptors for vitamin D and the capacity to metabolize it.

So far, vitamin D has been found to stimulate production of substances that act as the body’s own antibiotics, killing off pathogens. But that may be just the start of it. Low levels of the vitamin are regularly found among those with respiratory and other infections. There is an inverse relationship between upper respiratory tract infection and blood levels of vitamin D.

Whether or not vitamin D deters infection, it has been shown to mitigate disease severity. It puts a leash on the production of pro-inflammatory responders. That has trained attention on it during the pandemic, as runaway inflammation is linked to the most dire COVID-19 consequences. It also makes the vitamin D status of Americans troubling. The NHANES study found that 95 percent of American adults get inadequate amounts of the nutrient.

The mineral zinc takes yet a different approach to immunity. Supplied to the American diet primarily in red meat, it contributes to both innate and adaptive immunity. The mineral gets first immune responders to the site of infection and, once there, keeps inflammation from flaring out of control. Without zinc, the immune response becomes overzealous and tissue-destructive. Zinc also influences the activity of adaptive immunity’s T cells as they customize to target specific antigens on invading pathogens.

Zinc deficiency is known to increase susceptibility to infection. According to the NHANES study, 15 percent of Americans have insufficient intake of zinc. Researchers estimate that among the elderly, 40 percent are outright deficient. Taken in the form of lozenges, zinc supplements shorten the duration of colds. The verdict is still out whether they can ward them off altogether.

And then there’s elderberry. Not a nutrient, it is a traditional remedy for viral respiratory illness, and COVID-19 has heightened interest in it. The fruit of the Sambucus tree, elderberry is loaded with antioxidants. In one randomized clinical trial, it limited the duration and severity of colds among air travelers. But exactly how it might work is unclear.

The more scientists probe the immune system, the greater the complexity revealed. But a simple fact remains: Immunity often needs a boost to be ready for the seasonal slew of microbes that become our aggressors.

Immunity In Mind

• The immune system and the emotional system are both channels facilitating our adjustment to a highly dynamic world.
• The brain and the immune system are not simply parallel processors of adaptation to environments; the two systems are connected physically as well.
• Both the autonomic nervous system and the neuroendocrine system link the brain and the immune system.
• Inflammation plays a major role in depression through the immune response to stress.
• The risk of depression is high in diabetes, cardiovascular disease, infections, and autoimmune disorder—all conditions with an inflammatory component.
• Cognitive behavioral therapy has been shown to reduce harmful immune responses, such as the production of proinflammatory cytokines.
• Psychotherapy with a group component has been found to enhance immune function.