This text was initially featured on The Dialog.
A longstanding medical fantasy means that taking vitamin B1, often known as thiamine, could make your physique repel mosquitoes.
A “systemic repellent” that makes your complete physique unappealing to biting bugs actually sounds good. Even in case you accurately reject the misinformation questioning secure and efficient repellents like DEET, oral repellents would nonetheless have the profit that you simply wouldn’t want to fret about protecting each inch of uncovered pores and skin or carrying containers of bug spray everytime you enterprise into the nice open air.
Together with thiamine, different alleged oral mosquito repellents embrace brewer’s yeast, which accommodates thiamine, and garlic, the legendary vampire repellent. If oral repellents sound too good to be true, it’s as a result of they’re.
As a professor of entomology in Taiwan, the place the mosquito-transmitted Dengue virus is endemic, I used to be curious what science actually says about food-based repellents. After a really deep dive into the literature and studying virtually each paper ever written on the topic, I compiled this data into the primary systematic assessment of the topic.
The scientific consensus is, unequivocally, that oral repellents don’t exist. Regardless of intensive searches, no meals, complement, remedy, or situation has ever been confirmed to make individuals repellent. Folks with vitamin B1 deficiency don’t appeal to extra mosquitoes, both.
So the place did the parable that mosquitoes hate nutritional vitamins come from, and why is it so arduous to exterminate?
Making of a fantasy
In 1943, Minnesota pediatrician W. Ray Shannon gave 10 sufferers various doses of thiamine, which had solely first been synthesized seven years prior. They reported again that it relieved itching and prevented additional mosquito bites. In 1945, California pediatrician Howard Eder claimed 10 milligram doses may shield individuals from fleas. In Europe within the Nineteen Fifties, doctor Dieter Müting claimed that each day 200 milligram doses stored him bite-free whereas vacationing in Finland, and hypothesized a breakdown product of thiamine was expelled by way of the pores and skin.
These findings drew speedy consideration, and nearly rapid repudiation. The U.S. Naval Medical Analysis Institute tried to copy Shannon’s findings, however failed. By 1949, Californians utilizing thiamine to repel fleas from canine had been reporting it as “fully nugatory.” Managed research from Switzerland to Liberia repeatedly failed to seek out any results at any dose. The primary scientific trial in 1969 concluded definitively that “vitamin B1 will not be a systemic mosquito repellent in man,” and all managed research since counsel the identical for thiamine, brewer’s yeast, garlic, and different options.
The proof was so overwhelming that, in 1985, the U.S. Meals and Drug Administration declared all oral insect repellents are “not usually acknowledged as secure and efficient and are misbranded,” making labeling dietary supplements as repellents technically fraud.
Medical mechanisms aren’t there
Scientists know rather more about each mosquitoes and nutritional vitamins at this time than ever earlier than.
Vitamin B1 doesn’t break down within the physique and has no identified impact on pores and skin. The physique strongly regulates it, absorbing little ingested thiamine after the primary 5 milligrams and rapidly excreting any extra by way of urine, so it doesn’t construct up. Overdose is nearly unattainable.
As in people, thiamine is an important nutrient for mosquitoes. There isn’t any motive they might worry it or attempt to keep away from it. Neither is there proof that they’ll scent it.
The perfect sources of thiamine are complete grains, beans, pork, poultry and eggs. If consuming a carnitas burrito received’t make you repel mosquitoes, then neither ought to a tablet.
What explains the early experiences, then? Together with shoddy experimental design, many used anecdotal affected person experiences of fewer chunk signs as a proxy for lowered biting, which isn’t a great way to get an correct image of what’s occurring.
Mosquito bites are adopted by two reactions: an instantaneous response that begins quick and lasts hours and a delayed response lasting days. The presence and depth of those reactions relies upon not on the mosquito, however by yourself immune system’s familiarity with that individual species’ saliva. With age and continued publicity, the physique goes from no response, to delayed response solely, to each, to rapid response solely, and finally no response.
What Shannon and others thought was repellency may have been desensitization: The sufferers had been nonetheless getting bitten, they simply stopped displaying signs.
So, what’s the issue?
Regardless of the scientific consensus, a 2020 survey of pharmacists in Australia discovered that 27% had been nonetheless recommending thiamine as a repellent to sufferers touring overseas: an unacceptable suggestion. Apart from losing cash, individuals counting on nutritional vitamins as safety towards mosquitoes can nonetheless get bitten, doubtlessly placing them prone to ailments like West Nile and malaria.
To get across the American ban and broadly agreed-upon scientific consensus on oral repellents, some unscrupulous sellers are making thiamine patches and even injections. Sadly, whereas thiamine is secure if swallowed, it can trigger extreme allergic reactions when taken by different routes. These merchandise are thus not solely nugatory, but additionally doubtlessly harmful.
Not each drawback will be solved with meals. Lengthy sleeves and bug spray containing DEET, picaridin or different confirmed repellents are nonetheless your finest protection towards biting pests.