Colds are a common curse of winter, bestowing the miseries of coughing, congestion and assorted aches and pains. But few people realize that the viruses may affect their brains as well as their bodies.
"The sort of cognitive impairment you see from a common cold is in the same ballpark with the consumption of alcohol, working at night or working for prolonged hours," says Andrew Smith, PhD, a psychology professor at Cardiff University in Wales who has researched the cognitive effects of colds for more than 25 years. "Activities where safety is critical, like driving or operating dangerous machinery, may be impaired when you have a cold."
Researchers have explored not only the cognitive effects of colds but also how some people may be more or less susceptible to catching them. New research finds that parenthood and a positive outlook may help protect against colds, while stress can undermine the immune system's effectiveness in fighting off viruses.
In a study published last year, Smith had 189 participants complete a series of baseline cognitive tests. Then, over the next 90 days, one-third of them returned to the lab after they had developed a cold, while the remaining healthy participants served as the control group. The participants with colds reported less alertness, more negative moods and sluggish thinking. A second round of tests showed they also had slower reaction times and were slower at learning new information and completing tasks involving verbal reasoning and semantic processing (Brain, Behavior, and Immunity, 2012).
Research suggests that cold viruses cause sluggishness by interfering with neurotransmitters, perhaps affecting the transmission of noradrenaline, choline and dopamine. Noradrenaline is associated with reaction times. Choline has been linked to the encoding of new information, while dopamine affects working memory speed.
Previous studies have found that cognitive impairment can occur for people with infections from cold viruses even if they have no physical symptoms and that their decline in alertness can have serious consequences. Smith also conducted a study of 15 participants with colds and 10 healthy participants who completed a simulated driving task. Those with colds responded more slowly to unexpected events on the road and were less likely to detect collisions (BMJ Open, 2012). Another study, commissioned by Lloyds TSB Insurance, estimated that in 2008, more than 125,000 accidents in Great Britain were caused by drivers who had a cold or the flu.
The power of parenthood
While viruses can infect anyone, a new study finds that parents may have some extra resistance to colds, says Sheldon Cohen, PhD, who directs the Laboratory for the Study of Stress, Immunity and Disease at Carnegie Mellon University. In a study with 795 participants, Cohen found that parents age 25 or older were less likely to develop colds after they were exposed to viruses than were people with no children, although parenthood didn't help protect parents ages 18 to 24 from colds (Psychosomatic Medicine, 2012). Older parents were less susceptible to colds regardless of whether they were married or whether their children still lived at home. The benefit of being a parent was independent of antibody levels to the cold virus, indicating that the association was not attributable to parents' developing more immunity by being exposed to viruses their children brought home.
The study didn't explain why older parents were less susceptible to colds, but the researchers theorize that parenthood may produce feelings of purpose in life and positive emotional experiences that help boost their immune systems. Younger parents may not receive the same protective benefit against colds because they are less prepared psychologically and economically to be parents and may feel more overwhelmed, Cohen says.
A positive emotional style or outlook on life may also help ward off colds, according to another of Cohen's studies. His research team measured emotional styles of 193 participants who were later exposed to a cold or flu virus through nasal drops. Although 81 percent of the participants were infected, only a third developed colds with physical symptoms. The people with more positive emotional styles were less likely to get colds or the flu and reported fewer symptoms than expected when they did get sick (Psychosomatic Medicine, 2006).
A wealth of research has explored how stress can wreak havoc on the immune system, which may lead to more colds and more severe physical symptoms. "There is a really potent effect for people who have suffered from stress that lasts a month or longer," Cohen says. "They are basically more likely to get sick."
In one of Cohen's studies, people who suffered from long-term interpersonal stressors, such as a bad marriage or work conflicts, were two-and-a-half times more likely to get a cold than people without those stresses (Health Psychology, 1998). People who were unemployed or underemployed had it even worse: They were almost five times as likely to develop a cold.
The stressed participants often engaged in unhealthy activities, such as smoking or skipping exercise, but those factors didn't explain the relationship between stress and colds, Cohen says. That relationship may be triggered at the molecular level by cytokines, proteins that serve as messengers to help stimulate the immune system's response to infection. The physical symptoms of a cold aren't caused directly by the virus, but instead by the immune system's response to the foreign invaders, which includes the release of cytokines, Cohen says. These protein molecules help fight the cold virus, but they also cause runny noses and congestion.
When people are chronically stressed, they produce too much cortisol, a hormone that usually helps regulate the level of cytokines. The heightened hormone levels cause immune cells to gradually become insensitive to cortisol, triggering the release of more cytokines that exacerbate the cold symptoms, Cohen says.
Of course, the impact that stress has on the common cold is just one facet of the research psychologists are doing in the field of psychoneuroimmunology — exploring the relationship between the mind and the immune system. In today's era of more integrated care, psychologists now have broader opportunities to do interdisciplinary work in that field.
"The biomedical community is more accepting of the fact that behavioral influences on the immune system make a difference," says Janice Kiecolt-Glaser, PhD, a psychology and psychiatry professor at Ohio State University who studies the effects of stress on the body. "Behavior is really recognized now as an important player in terms of health."
Brendan L. Smith is a writer in Washington, D.C.