Colds is the mild viral infection that people get during cold weathers like winter; it affects the nose and respiratory passages and produced by very low environmental temperatures. Published in the Proceedings of the National Academy of Sciences, a new research now explains why people get colds during cold weather.
The study reveals that people get common cold when internal body temperatures fall after exposure to cold air – and this causes a corresponding fall in the immune system’s ability to fight the rhinovirus that causes common cold. And the next thing that happens is that you start to sniffle.
According to Akiko Iwasaki, a professor of immunobiology at Yale University School of Medicine, “It has been long known that the rhinovirus replicates better at the cooler temperature, around 33 Celsius (91 Fahrenheit), compared to the core body temperature of 37 Celsius (99 Fahrenheit). But the reason for this cold temperature preference for virus replication was unknown. Much of the focus on this question has been on the virus itself. However, virus replication machinery itself works well at both temperatures, leaving the question unanswered.”
To further establish the relationship between internal body temperatures and the ability of the body to fend off a virus, researchers incubated two groups of mouse cells in two different temperatures. One cell group was incubated at 37C or 99F – the temperature found in the lungs, and the other group incubated at 33C or 91F to resemble that of temperature found in the nose. When eventually exposed to rhinovirus – the mild virus that causes common cold – the researchers found that internal body temperatures have no direct effect on the virus at all; but then, the body’s indirect immune system responds to the presence of the virus in various ways – a stronger response is found within warmer lung cells and a weaker response noted from colder nasal cells.
Iwasaki explained that “We used mouse airway cells as a model to study this question [and found that] at the cooler temperature found in the nose, the host immune system was unable to induce defense signals to block virus replication.” He added that “By inhaling the cold air from the outside, the temperature inside the nose will likely decrease accordingly, at least transiently. Therefore, an implication of our findings is that the cooler ambient temperature would likely increase the ability of the virus to replicate well and to develop a cold. However,” he added, “our study did not directly test this; everything was done in tissue culture dishes, and not in live animals exposed to cold air.”
A medical epidemiologist with the US Centers for Disease Control and Prevention’s division of viral disease, Dr. John Watson, states that “Why exactly people get colds is hard to assess,” he noted. “What is well-established is that the common cold is extremely common. We can say that adults get it in the area of three times every year. And for kids under 6 it may happen twice as often at that.”
Since there are over 100 different types of rhinoviruses, they are all typically mild but most affect the upper respiratory system while some the lower respiratory tract. “Who gets what and why is incompletely understood,” Watson said. “There are certainly some clear risk factors. People with immune-compromising conditions or preexisting illness face a higher risk, as do the elderly and premature babies. But pointing to cold weather itself is not a simple matter,” he added. “It may be cold itself. Or it may be that people’s behavior in cold weather changes, and those changes – such as being more likely to congregate indoors with other people in smaller spaces – could put people at an increased risk, rather than the cold itself.”
And as a parting shot from Watson, he added that “It’s an interesting finding and probably worthy of additional study. But it is certainly not a settled question.”