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Make Mosquitos Like You Less

Surprising dietary remedies to keep away our biting friends. This episode features audio from:

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Today – we hear about dietary remedies that encourage mosquitos and ticks to find a meal elsewhere.

Are some people just more attractive to mosquitos than others? Apparently so, as identical twins are most likely to be similarly tasty, compared to fraternal twins who only share 50 percent of their DNA––demonstrating an underlying genetic component that can be sniffed out by mosquitoes, although it’s not clear if it’s because some people smell better, or other people just smell worse.

We know pregnant women are twice as attractive to malaria mosquitoes and also that mosquitoes are attracted to sweat. Human sweat contains components that are attractive to anthropophilic—meaning human-loving—mosquitoes. The unique composition of human sweat appears to explain its tantalizing effect, though sweat from some body parts is evidently more tantalizing than others. Skin emanations collected from armpits were less attractive compared to hands or feet. They think the difference may be caused by deodorant residues, since in a subsequent experiment, volunteers were asked to avoid using skincare products for five days, and after that, no differences were detected.

The creepiest bit of research I found was this. The parasites that cause the mosquito-borne disease malaria, which kills hundreds of thousands of people a year, makes you more attractive to, you guessed it, the mosquitoes that transmit malaria. What better way for the parasites to hitch from person to person. Instead of leaving it up to chance, some parasites manipulate their hosts in elaborate ways. I’ve talked about how the toxoplasma brain parasite draws mice to the smell of cat urine to get into cats’ brains. Or, how about the rabies virus concentrates in the saliva while tapping into the Cujo rage circuits in the brain. There’s even a parasite that needs to get from an ant to a bird; so, it turns the ant’s belly bright red to look like a ripe berry and makes the ant stick it up into the air to confuse fruit-eating bird. Here’s the ants before and after infection. Just like malaria parasites making us particularly tasty to mosquitos.

Anything we can do to make ourselves less tasty? I’ve talked about the various mosquito repellents you can spray on your skin––both synthetic and natural mosquito repellents. But is there anything you can eat or drink to make you less of a target?

When you search the scientific literature for diet and mosquitoes, a lot of articles like this pop up, on diets for mosquitoes, like SkitoSnack for that artificial blood meal replacement. Feeding mice different diets makes a difference. But what about people?

One of the most common anecdotes is that vitamin B complex supplements protect against biting insects. Other anecdotal remedies include the taking of garlic, marmite, Vegemite, brewer’s yeast tablets, and alcohol. But you don’t know, until you put it to the test.

How about a randomized, double-blind, placebo-controlled trial of garlic as a mosquito repellent? A belief in the ability of garlic to repel insects seems to be widespread; so, researchers in Connecticut decided to see if it were true. They looked at the numbers of mosquitoes that did not feed on the subjects, the number of mosquito bites, the weights of the mosquitoes after feeding, and the amounts of blood ingested were all determined on people on and off garlic. And, the data did not provide evidence of significant mosquito repellence.

No surprise, given that even if you slather garlic oil on your skin, within 30 minutes mosquitoes don’t seem to care. Eating garlic may, however, help against ticks. Because military personnel can sometimes be at particularly high risk for tick bites and tick-borne diseases, the Swedish military conducted a randomized controlled double-blind trial of garlic to prevent tick bites among marines. Fifty swallowed the equivalent of about a clove a day of garlic, and fifty took placebo pills. Then, they all switched. And, there was a significant reduction in tick bites when consuming garlic compared with placebo–cutting the risk of tick bites by about 20 percent.

Twenty percent is better than nothing, but treating your clothing with something like permethrin has been shown to be 100 percent effective against deer ticks, the vector of Lyme disease. And so, that may be better than counting on garlic bread to save you.

In our next story – what happens when mosquitos put on beer goggles? 

An online survey of personal mosquito-repellent strategies unearthed all sorts of strange stratagems, from cutting a tomato in half and leaving it next to the bed, to rubbing yourself with cigarette butts soaked in alcohol. You could also soak yourself in alcohol with a gin and tonic, cut down on sugar, cut out meat, or bananas. But what’s funny is some say avoid bananas, some say eat bananas to stave off mosquitos, and others say topically rub them on your skin. (I don’t even want to know about what else you might do with them).

Eat bananas? Avoid bananas? You don’t know, until you put it to the test. The impact of the consumption of bananas on attraction of a malaria mosquito to humans. Researchers in Wisconsin randomized subjects to eat grapes or bananas before testing what they then tasted like to mosquitoes, and the ingestion of bananas was strongly associated with an increase in the number of mosquito contacts for hours after eating a banana––translating to about 11 extra contacts after one hour and seven contacts after two hours. Meanwhile, the ingestion of grapes had no effect. Interestingly, it didn’t seem to matter how many bananas you eat at once, as eating three bananas didn’t appear to make people any tastier than eating one. Bottom line, after years of repeat experiments, they concluded that ingestion of bananas, but not grapes, resulted in significantly higher attraction of mosquitoes for hours after ingestion on average––though some people did appear to be immune to the banana effect.

What about that gin and tonic? Some have suggested alcohol will help keep the bugs away; others suggest we might suffer more mosquito bites after ingesting liquor. Well, there’s only one way to find out. Drink some beer and put your arm in a box with some mosquitoes. The title of the study gives it away. Alcohol ingestion stimulates mosquito attraction. About 40 percent of the mosquitoes landed on their arms before drinking a bottle of beer, compared to about 50 percent afterwards. And, it didn’t appear to have anything to do with changes in sweat production or skin temperature after the booze. It might just be something you start exuding after you drink. And so, it’s also not just because you got bit a bunch of times because you like blacked out in an alley or something. The researchers concluded that since the percent of mosquitos landing on volunteers significantly increased after beer ingestion, drinking alcohol stimulates mosquito attraction. But, it could just be drinking beer, not necessarily all alcohol. And they only tested one species of mosquito: the one that transmits diseases like dengue, zika, and yellow fever.

What about gauging human attractiveness to malaria mosquitoes, before and after volunteers consumed either beer (using 25 volunteers and a total of 2,500 mosquitoes) or water as a control, with 18 volunteers and only about 1,800 mosquitoes. And? Water consumption had no effect, but beer consumption increased the attractiveness of the volunteers. It’s like the mosquitos put on beer goggles. Beer consumption increases human attractiveness.

To date, bananas and beer are the only dietary components that have been shown to increase mosquito attraction. Okay, but we want to repel mosquitos, not attract them. What about testing B vitamins as a home remedy against mosquitoes? B vitamins are often recommended in the popular media as a systemic repellent against mosquitoes, especially on the web. The first studies date back over a half century. They gave people doses of vitamins B1 and B6, yet in a series of subsequent tests the mosquitoes probed avidly and bit promptly. They only tested the vitamins on four people, but the vitamins appeared so useless, they didn’t think it worth repeating the experiments, in view of the obvious lack of repellency of these vitamins. We believe, the researchers wrote, that we have disproved the notions that vitamins taken orally act as mosquito repellents. But, they only tested vitamins B1 and B6. What about B2, B3, B5, B9, B12? You don’t know, until you put it to the test.

Vitamin B complex supplements are not effective as repellents. But, these studies were limited by the use of very few human subjects, only one species of mosquito, and a limited number of B vitamins. So, researchers decided to put it to rest once and for all. B1, B2, B3, B5, B6, B7 (also known as biotin), B9, B12. They also just tried a megadose of thiamine (B1), which is rumored to be the most effective B and…nothing. No effect of vitamin B supplementation. Any of them. I mean, it would be nice to have an effective oral insect repellent. Unfortunately, vitamin B1 has been proved to be ineffective. And, this includes so-called mosquito repellent patches, that supposedly deliver B1 through the skin. No protection provided whatsoever.

Bottom line: Vitamin B1, also known as thiamine, is not a systemic mosquito repellent in men. They even tried smearing it on people’s skin. With failure after failure, you start feeling bad for the volunteers, seated in a room with their shirts off. Then, they just release 100 suckers into the room. Look at some of these bite rates. These are bites per minute. Up to 96 bites per minute. Just think how bad it would have been if they had some bananas and beer.

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