Have you ever wondered why people catch the flu right around this time of year? Fall and winter are the worst seasons for upper respiratory tract infections like colds or influenza. That’s true in Europe as well as North America. In the southern hemisphere (think Australia and New Zealand), it’s just the reverse. When it starts getting colder down under, around our spring and summer, they start sniffling and sneezing. Is there any way to prevent influenza wherever you live?
Why Do People Catch the Flu in Winter?
Researchers have been trying to answer this question for decades. There are several explanations, but none of them are well proven.
We Spend More Time Inside:
There’s no doubt that cold nasty weather tends to keep people inside. Closer contact with others could help spread viruses.
But most people work indoors both during the winter and the summer. School starts in August and September, but the flu doesn’t really get going until December. We have seen no data that suggest if you work outdoors you can prevent influenza.
The Bad Air Theory:
Then there’s the window theory of viral transmission. Some experts have proposed that people keep their windows open more in the summer and close them in the winter. Closed windows theoretically permit people to breathe virus-contaminated air more in the winter.
We think this theory is bogus. These days people at work and at home tend to rely on air conditioning in the summer. Windows stay closed all year round. Just try opening a window in a high-rise office or apartment building. It’s virtually impossible. The air continually circulates through the AC system in the summer and through the heating system in the winter. We haven’t seen any data showing that keeping windows open can prevent influenza.
Less Vitamin D in Winter:
Another possible explanation involves vitamin D. When people spend more time inside and wear warm clothes outside they get less sun exposure. That means they make much less vitamin D in the winter than in the summer.
This lack of vitamin D has been proposed as the reason people come down with more upper respiratory tract infections in the winter. Lower vitamin D levels mean lower immune function and potentially more vulnerability to viruses.
There are a couple of problems with this hypothesis, though. Dermatologists have admonished people to smear on the sunscreen as soon as the temperatures warm up. That prevents the body from making vitamin D. Since more people are taking vitamin D supplements all year round, why are we still getting sick in the winter?
A thorough review of the medical literature concluded that the results of vitamin D to prevent influenza were equivocal (International Journal of Molecular Sciences, Aug. 2018). Some research showed benefit. Other studies not so much.
“A survey of the literature data generates some controversies and doubts about the possible role of vitamin D for the prevention of influenza infections. However, there are data obtained in vitro or in vivo which denote the antiviral activity of vitamin D in the case of influenza. Nowadays, the final conclusion is that its significance as an anti-influenza agent remains unresolved, but it does not mean that these considerations are senseless. It is most important to realise that the broad spectrum of vitamin D activity does not exclude such a role.”
The authors note that:
“…it is unlikely that seasonal variations in vitamin D levels determine the seasonality of influenza in temperate regions.”
The Low Humidity Theory Gains Ground:
A less common theory involves humidity and heating systems. Forced hot air is usually low in humidity. Mouse research shows that dry air reduces resistance to influenza infection (Proceedings of the National Academy of Sciences, May 28, 2019).
An intriguing study found that low humidity, which is very common in heated buildings during the winter months, makes it easier for viruses to spread (PLOS One, Sept. 25, 2018). The scientists raised the humidity in half the classrooms of a community preschool.
In humidified rooms, the investigators found fewer influenza A viruses on toys and markers. Children in the non-humidified rooms had twice as many cases of influenza-like illness as those in the humidified classrooms.
Can Higher Humidity Prevent Influenza?
One place where infection control is critical is the hospital. A study conducted at the University of Chicago monitored microbes in a new hospital building starting two months before it opened and continuing for a year. Indoor conditions were monitored in both patient rooms and nursing stations.
The researchers suspected that hand washing, room cleaning technique or patient susceptibility would be major factors in the spread of infection. Instead, they discovered that relative humidity was a dominant contributor. When it fell below 40 percent, viruses and other pathogens were more likely to float around in the air successfully and find a target.
Since dry air also impairs the ability of the nose and skin to withstand viral invasion, there may be a double whammy. Patients in rooms with low relative humidity were more likely to develop healthcare-associated infections.
What does this mean for people at home? A few years ago, there was a rumor on the Internet that if people set an unpeeled onion out in a room, it would attract and trap influenza viruses. As far as we can tell, this is an urban legend.
If viruses survive and travel more easily in dry air, however, it may be helpful to humidify the air in hospitals, schools and nursing homes. This might help protect vulnerable people from respiratory illnesses that spread so easily in winter’s dry air.
Flu Shots to Prevent Influenza?
Public health officials say that vaccines are the best protection against influenza, but on average, flu shots only work for about 40 percent of those vaccinated. Some scientists have voiced concerns that this year’s influenza vaccine may not be as good a match to circulating viruses as we might hope. The 2019/2020 shot may not match the H3N2 virus that hammered Australia and could end up causing illness in North America. While it can be helpful to get a flu shot, additional measures may boost its benefits.
Washing hands, wearing a face mask and increasing the humidity in your home between 40 and 60 percent may all improve your chances of staying healthy this winter.
If all else fails, there are antiviral medicines that can modestly improve recovery time. They include oseltamivir (Tamiful) and the more recent baloxavir (Xofluza). You can learn more about the pros and cons of Xofluza at this link.
Final Thoughts on Ways to Prevent Influenza:
If you could relocate during winter months to a warm and humid climate, chances are pretty good that you might avoid the flu. Most of us do not have that luxury.
My mother grew up on a farm with a wood stove. There was always a kettle full of water sitting on the stove emitting steam and increasing humidity. Cod liver oil was a winter thing in those days. Perhaps the omega 3 fatty acids plus the extra vitamin D were helpful in improving immunity. Judging from the available science, it will be years before we have a scientific answer to their effectiveness.
In the meantime, wash your hands, wear a surgical mask and consider drinking some of Dr. Tieraona Low Dog’s Immuno-Tea. It contains:
- 1 ounce astragalus root, dried and sliced
- 1 ounce schizandra fruit, dried
- 1 ounce rose hips, dried
- 1/2 ounce eleuthero root, dried and sliced
- Honey and lemon to taste
Mix herbs together and store in a jar. Keep in a dark place.
To prepare: put one tablespoon herb mixture into two cups water, bring to a boil, and simmer for 15 minutes. Strain. Add honey and lemon to taste. Drink half a cup two to three times per day during the cold and flu season”
You can find Dr. Low Dog’s other recipe for Thyme Cough Syrup and my mother’s (Helen Graedon’s) chicken soup recipe in our book Recipes & Remedies from The People’s Pharmacy.