The Cold and A Cold: Do they really go hand-in-hand?

By: Helen Beilinson and Zuri Sullivan

Biology is complex—very, very, very, very, very complex—and because of this, simplification is incredibly important. Many experiments are conducted by breaking down a complex system and studying its constituent parts, manipulating specific components (or “variables,” in science slang) to understand how they impact the system as a whole. For example, to understand how viruses replicate within their animal hosts, scientists often study how the virus replicates in animal cells grown in an incubator, instead of the whole organism. As a consequence, scientific knowledge accumulates in tiny increments—each study answers a small, but specific question. When we amass sufficient answers to simple questions, we learn something new about a complex biological system. 

This strategy of deconstruction and reconstruction has led to a number of important scientific discoveries, but it comes at a cost. Findings made in smaller systems can’t always be extrapolated to the larger system. Sometimes, these findings are really exciting, and they tempt us to jump to conclusions because of their potential impact on the larger system. This presents a major challenge to science reporters: keeping a story exciting at its beginning while resisting the temptation for overstatement. Some stories in the media meet this challenge better than others, but like all news, science news should be taken with a grain of salt—a scientist’s interpretation of his or her findings and their potential impact on society can vary widely from the interpretations of reporters.

As a case study for this idea, we investigated a recent high-profile story about the relationship between temperature and catching the common cold. The original study, published last month in the Proceedings of the National Academy of Sciences by a team of investigators headed by the laboratory of Akiko Iwasaki, an investigator of Howard Hughes Medical Institute and Professor of Immunobiology at Yale University, investigated the effect of temperature on protective immune responses to rhinovirus, the predominant causative agent of the common cold.

“It’s been known since the 1960s that the virus replicates better at nasal cavity temperature, which is around 33 to 35 degrees Celsius,” said Dr. Ellen Foxman, a post-doctoral fellow at Yale University who was the primary author of the study. Core body temperature for humans is 37 degrees Celsius (98.6°F), but inhaling cool air brings the temperature in our noses down to about 33-35 degrees Celsius (91.4-95°F)—the temperature at which rhinovirus grows best. By exploring the role of specific immune responses in a cell system, the study found that the temperature difference in viral replication was caused by a temperature-dependent difference in immune responses. Turns out, key immune responses against rhinovirus don’t work as well at 33-35 degrees as they do at core body temperature, so the virus is able to replicate more.

Given the implications of these findings (particularly that we should always listen to our moms and bundle up in cold weather), this study was covered widely by the media, with such headlines as “Common cold ‘prefers cold noses’” and “Common cold really is triggered by cold weather”.

“Some of the headlines went further than we did in our study,” says Ellen. “We didn’t actually study weather at all. Or people going out in the cold.” This was apparent in the original research findings, but many journalists bit into the cold weather/cold virus relationship. “To really make that claim, in terms of a clinical research study, you’d need to have two groups of people, normalize them, put some people in the cold…all that we didn’t do. So some people took it a bit further than we would have.”

This study wasn’t conducted in humans or in animals for that matter. It was done in a system where cells that live on a dish in an incubator in a lab are infected with the virus and are grown at different temperatures. Organisms are a lot more complicated than cells in a dish, making it difficult to extrapolate the findings from the study to a complex organism like a human. The relevance of these studies in humans is not currently known. This was seen as a limitation in other mainstream articles that covered the study, but was never fully discussed. On another note, the study looked at temperatures of 33-35°C compared to 37°C. The temperature of the human nasal cavity during winter could reach far below 33°C. Studies exploring how the immune responses functions below 33°C have not been done. Far from invalidating their results, however, the controlled system in which the experiments were performed is a major strength of the research. It demonstrated that the slight shift in the temperature dampens the immune response to the virus. Because inhaling cold air results in cooling of the nasal cavity temperature, the study implies that the cold weather could lead to more virus replication in human nose.

“After we isolated the primary cells, everything was identical about them, except for a few hours of incubation at different temperatures. So, it’s not the same as studying it in a person…but in a person, there are so many variables that you can’t control, that you can’t analyze. That’s the advantage of doing something in a laboratory. You can control everything except for one variable at a time and see how this variable affects the immune response, and thereby the infection.” This high degree of control is an indispensable component of the scientific method—without it, results are extremely difficult to interpret because outcomes cannot necessarily be attributed to a single variable. In order to show cause and effect, scientists need to ask straightforward questions under tightly controlled conditions. This control allowed for the discovery of what Ellen sees as the most important implication of the study.