The reactions of our body when we are sick can be crucial in fighting infection. These changes can be critical to helping us improve faster.
We all know what it's like to be sick. We feel tired, perhaps a little depressed, less hungry than usual, more easily nauseated, and perhaps more sensitive to pain and cold.
The fact that the disease comes with a distinct set of psychological and behavioral characteristics is not a new finding. In medical terminology, the symptom of malaise covers some of the feelings that come with getting sick. Some use the term "disease behavior" to describe behavioral changes that occur during illness.
Health professionals often treat these symptoms as little more than side effects of having an infectious disease. But these changes can really be part of how we fight infection.
US researchers now propose that all these aspects of being sick are characteristic of a feeling they call "lassitude." And it is an important part of how humans work to recover from an illness. One study was published, in September, in the scientific journal Evolution and Human Behavior.
The body sets priorities
The human immune system is made up of a complex set of mechanisms that help suppress and eliminate organisms – such as bacteria, viruses, and parasitic worms – that cause infections.
Activating the immune system, however, uses up a lot of energy from your body. This presents a number of problems that your brain and body need to address to combat infection more effectively.
Fever is a crucial part of the immune response to some infections, but the energy cost to raise the temperature is particularly high. Is there anything you can do to reduce this cost?
Eating or not eating is a choice that affects your body's fight against infections. For one thing, foods provide energy to the body and some foods contain compounds that can help eliminate pathogens. But it also takes energy to digest food, which deflects resources from your total immune effort.
Researchers propose that the distinct changes that occur when we get sick help us solve these problems automatically. Of course these changes depend on the context. While it may make sense to reduce food intake to prioritize immunity when the patient has too many energy reserves, it would be counterproductive to avoid eating if the patient is hungry.
The disease as a feeling
So how does the body organize the beneficial responses to infection? The evidence analyzed suggests that humans have a regulatory program. When it detects signs of infection, the program sends a signal to various functional mechanisms in the brain and body. They, in turn, change operating patterns in useful ways to combat infection.
This type of coordination program is what some psychologists call sentiment: a developed computer program that detects indicators of a specific recurring situation. When a particular situation arises, feeling orchestrates relevant behavioral and physiological mechanisms that help solve the problems at hand.
Some of these coordination programs are in line with general intuitions about what constitutes a feeling. Others have functions and characteristics that we do not normally consider "emotional".
Some psychologists suggest that these programs probably evolved to respond to identifiable situations that occurred consistently over evolutionary time that would affect the survival or reproduction of those involved.
Researchers now apply the idea of these emotional programs to the experience of being ill and hope that it will help to solve problems of practical importance. From a medical point of view, it would be helpful to know when laxity is doing its job and when it is defective. Health care providers would have a better idea of when to intervene to block certain parts of lassitude and when to leave them alone.