Should we all take aspirin? Not so fast.

I thought we'd put this one to bed. A large-scale study showed that low-dose aspirin (one quarter of a standard 325 mg pill, or about 81 mg) taken once a day can prevent heart attacks and some common types of cancer, including colon cancer.

I wrote about this topic just over a year ago, and I've followed my own advice, taking daily 81mg aspirins since then. The US Preventative Services Task Force recommends this too: regular, low-dose aspirin for people between the ages of 50 and 69 helps to prevent heart attacks, strokes and some types of cancer.

But now, a new study just published in The Lancet upends that advice. It's not that the previous study was wrong–it wasn't. It's just that the effects of aspirin vary significantly based on body weight. Essentially, the new study finds, almost all of the benefits accrue to people who weigh 70 kilograms (154 pounds) or less.

The study, a re-analysis by Peter Rothwell and colleagues of ten large trials that included 117,279 participants, is too long and complex to summarize here, so I'll just highlight a few key points. (Because the paper is open access, anyone can read it for free, just by clicking here.)

The good news, for people who weigh between 50 and 70 kg (110-154 lbs), is that the benefits of daily low-dose aspirin are quite good, possibly even better than we thought. The relative risk of a heart attack, stroke, or other major heart-related event is about 25% lower for people in this group.

The bad news, for the rest of us, is that we seem to get no heart-related benefits from taking a daily low-dose aspirin.

So perhaps those of us who weigh more than 70 kg just need a slightly larger daily aspirin pill. There is some good news here: Rothwell and colleagues found that, indeed, higher doses of aspirin are effective at reducing the risk of heart attacks for people who weigh more than 70 kg. This makes sense: adjusting the dosage based on weight is how most drugs are given. The problem is that aspirin generally comes in only 3 pill sizes: 81, 325, and 500 mg. So the studies have only looked at these 3 doses, and 325 mg is likely too large a dose for most people, because it increases the risk of bleeding events.

What about the cancer risk? As I wrote in 2017, the biggest benefit from daily low-dose aspirin is its reduction in the risk of colon cancer, breast cancer, and prostate cancer. Here, the new study doesn't quite give the whole picture, because it didn't look at breast cancer or prostate cancer. For colon cancer, low-dose aspirin reduces the risk significantly for people who weigh less than 70 kg. For heavier people, low-dose aspirin had little to no effect on colon cancer risk, but regular-sized aspirin (325 mg) worked for people up to 80 kg (176 lbs).

What to do now? The new study concludes that:
"The one-dose-fits-all strategy for daily aspirin use is unlikely to be optimal."
 In other words, you will probably benefit from daily aspirin, but the amount you should take depends on your weight. If you weigh less than 70 kg, the 81-mg tablets that you can find almost anywhere will do nicely. 

But what if you weigh more (as most men and many women do)? The science doesn't yet give us an answer: you could simply take 2 low-dose pills a day, but too much aspirin increases the risk of serious bleeding events. You could instead take a few extra pills per week, depending on your weight, which is what I'm going to do, at least until we get better data and more precise guidelines.

(Final note: as always, before you make any changes in your medication, ask your physician.)

Mosquito wars: what works to keep these little buggers away?

It's summer time, and with it comes outdoor dining, sports, and strolls through the neighborhood. But the loveliest evening can be spoiled by mosquitos, who torment us as they suck our blood and leave itchy welts behind.

How can we keep these pests away? Do citronella candles work? How about Victoria's Secret Bombshell perfume? (No, I'm not kidding. Read on.)

First, about mosquitos: they are more than just a nuisance. They also carry diseases, including West Nile virus, which now affects the entire U.S., and far more deadly diseases in other countries, including malaria, yellow fever, and Zika virus.

(Aside: West Nile virus first appeared in the U.S. in 1999, in New York, after a mosquito apparently hitched a ride on a plane from somewhere in the Middle East. A few years later it started spreading rapidly across the country, and now it's basically everywhere. West Nile fever usually manifests as a flu-like illness, but about 1 in 150 people get severe, life-threatening symptoms.)

One of the most popular ways to keep mosquitos off the backyard patio is easy to spot on a summer night in my neighborhood: burning citronella candles (such as this one from Cutter), which contain a natural oil made from grass whose scent is supposed to repel mosquitos. These are very popular and widely sold, but do they work?

Fortunately, the Journal of Insect Science published a study just last year, by Stacy Rodriguez and colleagues from the University of New Mexico, that gives us an answer. The scientists purchased a dozen different products, all from Amazon or local stores, and ran a very nice experiment to figure out how well each product worked.

Here's the setup: the scientists placed a cage full of mosquitos near a human volunteer, who sat 1-3 meters away, with a gentle breeze blowing from the humans towards the mosquitos. (This made it easier for the mosquitos to smell the humans, and also meant that they had to fly against the breeze if they wanted to bite the subjects.) The scientists applied each mosquito repellent (or device) to the volunteers, opened the cage, and counted how many mosquitos were attracted. They also ran controls where the subject had no protection.

So what worked? First off, with no protection, about 88% of the mosquitos were attracted to the human subjects. The three products that worked best at repelling mosquitos were:

  1. OFF!® Clip On™, where just 27% of the mosquitos were attracted
  2. Cutter® Lemon Eucalyptus, with 30%, and
  3. Ben’s® Tick & Insect Repellent, with 34%. 

Nothing else worked nearly as well as these, although several products reduced the proportion of mosquitos from 88% down to 60-70%.

Notably, some of the products did not work at all, including citronella: Cutter Citro Guard had no effect on the mosquito's attraction to the human volunteers. Other failures were Invisaband™ and Mosquitavert, wrist bracelets containing geraniol oil, and the PIC® Personal Sonic Mosquito Repeller, a clip-on ultrasonic device that emits a sound that mosquitos presumably don't like. Mosquitos basically ignored these devices.

So what's the secret in the products that do work? The OFF! device contains metofluthrin, which appears to be the most effective repellent on the market. Lemon eucalyptus oil is a natural product that is nearly as effective, and Ben's Tick & Insect Repellent contains DEET, which has long been known as an effective defense against mosquitos.

The only one of these products that purports to work on a whole area (like your backyard patio) rather than just one person is the citronella candle, which unfortunately just doesn't work. So if you want your garden party guests to be protected, you may have to keep on hand a basket full of products with metofluthrin, lemon eukalyptus oil, or DEET.

And what about Victoria's Secret Bombshell perfume? Well, the same scientists looked at Bombshell in a 2015 study, where they included the perfume thinking that it would attract (rather than repel) mosquitos. Surprisingly, it had the opposite effect: even though DEET and metofluthrin are more effective, the scientist found that:
"Victoria Secret Bombshell repelled mosquitoes quite effectively 120 min post application."
And what is the active ingredient? According to the same study, that's unknown.