What's the proper amount of dog for optimal health?

Humans have had dogs as companions for thousands of years. Over that time, dogs have evolved to become ever-better companions, as we humans selectively bred them for traits that we like, such as friendliness and loyalty.

Dog owners already know that owning a dog reduces stress. But it turns out that the health benefits of owning a dog go quite a bit further: two new studies published this month in the journal Circulation both found that owning a dog reduces your risk of dying.

The first study, by Carolyn Kramer and colleagues at the University of Toronto, reviewed ten other studies dating back more than 50 years, covering 3.8 million people. They compared dog owners to non-owners and found that dog owners had a 24% lower risk of dying, from any cause, over a 10-year period. The benefit was even greater for people who'd suffered a heart attack: those who had a dog at home after their heart attack had a 65% lower risk of dying.

The second study, by Tove Fall and colleagues at Uppsala University, focused on the benefits of owning a dog for people who have had a heart attack or a stroke. They used the Swedish National Patient Register to identify 335,000 patients who'd suffered one of these events between 2000 and 2012, about 5% of whom were dog owners. They found even greater benefits than the first study: among people who'd had a heart attack, their risk of dying was 33% lower if they owned a dog as compared to people who lived alone. The benefits were smaller but still significant for people who lived with a companion (a spouse or a child): they still had a 15% lower risk of dying if they also owned a dog. For those who'd had a stroke, the risk of dying for dog owners was 27% lower than for people who lived along, and 12% lower than for people who lived with a companion but didn't have a dog. This study measured the risk over a 4-5 year followup period.

These studies are consistent with many other scientific reports, stretching back decades. They're all consistent, and they all point in the same direction: dog ownership is good for your health. In fact, back in 2013 the American Heart Association issued an official statement on "Pet Ownership and Cardiovascular Risk" with this recommendation:

"Pet ownership, particularly dog ownership, may be reasonable for reduction in cardiovascular disease risk."

However, because the evidence was not very strong, the AHA also advised that people shouldn't get a pet "for the primary purpose of reducing CVD risk." In other words, don't get a dog if you don't want one. As every dog owner knows, owning a dog is much more trouble than simply taking a daily pill.

The new studies strengthen the existing evidence for the health benefits of owning a dog. In an accompanying editorial in Circulation, Dhruv Kazi from Harvard Medical School asks a critical question: is the association between dog ownership and reduced mortality just a correlation, or is it causal? He points out that studies have shown that dog ownership reduces blood pressure and other signs of stress, and that dog owners tend to get outside and walk more (with their dogs). Thus it's very plausible, medically speaking, that dog ownership is good for you. For these and other reasons, Kazi concludes that

"the association between dog ownership and improved survival is real, and is likely at least partially causal."

One final question is still nagging at me, though. Now that we know that dog ownership is good for your health, what's the optimal dose? Would it be even healthier to own two dogs rather than one? And what if we throw in a cat, does that strengthen or reduce the effect? Finally, is it healthier to own a larger dog, or is a small one just as good?

Clearly, more research is needed.

[Note: the author discloses that he owns a rescue dog, a rather small terrier.]

Can You Improve Your Memory With A Jellyfish Protein?

Some colleagues of mine recently asked me about Prevagen, a supplement that is being advertised heavily on television as a memory booster. It's everywhere, they said–but what is it? And does it work?

Both questions are pretty easy to answer. On the first question, the TL;DR version is that Prevagen's primary ingredient is a protein called apoaequorin, which is found in a species of jellyfish that glows in the dark. These jellies produce two proteins, apoaequorin and green fluorescent protein (GFP), that help them fluoresce. It’s an amazing biological system, and the three scientists who discovered and developed the chemistry of GFP were awarded the 2008 Nobel Prize in chemistry.

Cool science! But what does this have to do with human memory? Not much, it turns out.

First let's examine what Prevagen's manufacturers, Quincy Bioscience, say about it. Their website claims that:

"Prevagen Improves Memory* 

Prevagen is a dietary supplement that has been clinically shown to help with mild memory loss associated with aging.* Prevagen is formulated with apoaequorin, which is safe and uniquely supports brain function.*"

Sounds pretty clear, right? But note the asterisks by each of these claims: if you scroll all the way down (or read the small print on their packages), you'll find out that:

"*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease."

You may recognize this language: it's what all supplement manufacturers use to avoid getting in trouble with the FDA. It means, essentially, that the government hasn't approved Prevagen to treat anything, including memory loss.

Despite Quincy’s claims, I see no reason why eating this protein would have any effect at all on brain function. First of all, it’s not even a human protein, so it's unlikely to work in humans. Second, even if it did work in humans, eating it would not deliver it to our brains, because it would be almost certainly be broken down in the stomach. And third, the connection between any protein and memory is very complex, so simply having more of a protein is very, very unlikely to improve memory.

Quincy's website points to a single study that they themselves conducted, which they argue showed benefits for people with mild memory impairment. However, others have pointed out that the experiment (which was never published in a scientific journal) didn't show any such thing: overall there was no difference between people who took Prevagen and those who took a placebo, but the manufacturer's did some p-hacking to extract a subgroup that appeared to get a benefit. As Dr. Harriett Hall and others have pointed out, this kind of p-hacking is bogus.

And what about my observation that the jellyfish protein will simply be digested in the stomach, and never make it to the brain? It turns out that the company itself admits that I'm right. On their website, they have a "research" page pointing to several safety studies, designed to show that Prevagen won't cause an immune reaction. One of these studies explains that

"Apoaequorin is easily digested by pepsin."

Pepsin is the chief digestive enzyme in your stomach. So Prevagen's main ingredient never gets beyond the stomach, which is why it's probably quite safe. (Joe Schwarcz at McGill University recently made the same point.)

Back in 2015, I asked Ted Dawson, the Abramson Professor of Neurodegenerative Diseases at Johns Hopkins School of Medicine, what he thought of Prevagen’s claims.

“It is hard to evaluate Prevagen as to the best of my knowledge there is no peer-reviewed publication on its use in memory and cognition,” said Dawson. “The study cited on the company’s web site is a small short study, raising concerns about the validity of the claims.”

Finally, a word to those who are still tempted to try Prevagen: it isn't cheap. Their website charges $75 for a bottle of 60 pills, each containing 10 mg of apoaequorin, or $90 for 30 pills of the "Professional formula," which contain 40 mg. (Note that there's no evidence that taking a higher dose will work any better.)

The FTC sued Quincy Bioscience in 2017 for deceptive advertising, arguing that claims that Prevagen boosts memory are false, and that claims it can get into the brain are also false. Just a few months ago, a judge ruled that the case can proceed. Meanwhile, though, the advertising and sales of Prevagen continue. The FTC case states that Quincy sold $165 million worth of Prevagen in the U.S. from 2007 to 2015.

So the bottom line is: jellyfish proteins are very cool, but eating them won't improve your memory. If you're interested in brain food, perhaps you just eat more fish, which might actually work.

(Note: I wrote about Prevagen in 2015, and some elements of this article are based on my earlier one.)