The Biting Arthropods: Natural isn't always better

Here in Skepticville we have been hearing daily reports about people being struck down by West Nile Virus (Link) and so at dusk people are avoiding their porches and avoiding having pool parties and grilling outside in order to avoid the pesky mosquitoes.  (It's also extremely hot here, even at dusk, so many people are avoiding the porch to seek air conditioning inside).    Now of course with reports of the outbreak come a host of "natural" alternatives.

Some of the "natural" alternatives involve fixing screens in the house, getting rid of standing water, and not being outside if possible at dawn and dusk.  Chances are even the most skeptical among us would see the value of fixing screens that need to be fixed anyway, avoiding the time when mosquitos are most active, and trying to keep them from breeding.  Our entomology friends will tell us that lactic acid (strong evidence) and carbon dioxide (weaker evidence), which we humans naturally produce, more so when we exercise, also serve to attract mosquitoes.  (Read more about how the entomologists have been examining human attractants here.  Certain kinds of mosquitoes are attracted to dark clothing and foliage (Link.)  Once again, science has come to our rescue in helping us evaluate simple things we can do to prevent mosquito borne illnesses.

Why is SkepticRD writing about this on a nutrition blog?  Because many of the people who are seeking out "natural" remedies are trying to avoid the other recommendation given by the Centers for Disease Control (CDC):  wear insect repellant that contains N, N-diethyl-3-methylbenzamide, otherwise known as DEET.  Some of those remedies, include, you guessed it, certain foods that are supposed to help you repel the biting arthropods.
 

First of all, our northern friends in the Michigan Skeptics Association have already done quite a bit of work discussing the safety profile of DEET.    They have also collected some of the available data regarding one of the essential oils usually touted as a "natural" mosquito repellant, catnip oil.  Here at chemistry/about.com you can find a very well written letter toting why "natural" is not always better, especially when we don't have enough data regarding how much of that oil is safe to use (Link).

As far as the foods and vitamins are concerned, usually the foods/supplements people are told to consume to repel mosquitoes are onions, garlic, and vitamin B1.  Unfortunately, none of these claims have any scientific evidence to support it (Link).  Now, we know that science is often not enough to convince our non-skeptical friends to avoid doing crazy things, so is there any danger in eating or taking any of these alternatives?
 

Onions—other than the halitosis, eating onions at every meal will likely not hurt you.  Some people will experience bloating and gas from the sulfur that's found in onions, and some other people might experience a burning in the stomach.  This is more of a danger for people who take sulfur as a supplement than people who are eating the onions (you would think the bad breath might cause people to stop overeating, but you never can tell).  And please, if you are also trying to protect your cats and dogs from insect bites, DO NOT give them onions as onions contain thiosulphate which can cause their red blood cells to burst (hemolytic anemia).
 

Garlic—once again, except for the bad breath and possible flatulence, eating 2-4 garlic cloves per day will likely not hurt you.  Once again, the problem comes when people take garlic supplements.  Some people do get an upset stomach, bloating, bad breath, body odor, and there are rare but other possible side effects of garlic supplements like headache, fatigue, loss of appetite, muscle aches, dizziness described as vertigo, and allergies such as an asthmatic reaction or skin rash.  There are also several medications that can be affected by garlic supplements like birth control pills, blood thinners, and medications for HIV/AIDS.  If someone is taking aspirin or ibuprofen regularly w/garlic the risk of bleeding might also increase.  And if you are trying to protect your children from mosquitos, remember the safety profile for garlic tablets has not been evaluated in children! (Link)  Also, garlic has been touted as a “natural” insect repellant for your pets, but this could also be toxic to them as well.

Vitamin B1 (thiamine)—taking enough to achieve a toxic level in your blood is fortunately very rare with this vitamin.  Unfortunately, too much B1 can interfere with your body's ability to produce insulin and thyroid hormones, but this seems to happen at long term supplementation of 500 or more grams per day.  SkepticRD has usually seen tablets of the thiamine in 100 mg doses, but there are some tablets that contain 500 mg. Hopefully the signs of toxicity of shortness of breath, flushing, and fluid retention, etc would clue the person in that something is wrong, but I have learned not to underestimate the “more is better” philosophy of so many.  Keep in mind that you might also be "peeing away" the money you spent on supplements as excess B1 is excreted in the urine.
 

Bottom line—staying indoors and using DEET if you have to be outside, particularly in active mosquito time, is your best and still safest bet for avoiding the biting arthropods.