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.]

Play Tennis For A Longer Life. Science Proves It.

Chris Evert and former President George H.W. Bush playing
tennis at Camp David during Bush's presidency.

Tennis might just be the best thing you can do to extend your life.

A new study from Denmark, published just last week by Peter Schnohr and colleagues, shows that playing tennis may extend your life by nearly 10 years. That's a remarkably big benefit, one that even the study authors were surprised at.

It's been well-established for a while now that exercise helps you live longer. For example, the Cardiovascular Health Study found that people over the age of 75 can expect to gain 1 to 1.5 years of healthy living by being active rather than sedentary. Others studies have looked at the effects of running or walking and found similar positive benefits.

The authors of the new study wanted to look at other sports activities, not just running. Using a large cohort of 20,000 healthy people in the Copenhagen City Heart Study, they identified 8,577 who were in the study from the early 1990s until 2017 and who met a variety of other criteria for inclusion. This gave them 25 years of followup, long enough to ask the question: how does participation in sports affect life expectancy?

In particular, they looked at tennis, badminton, soccer, jogging, cycling, calisthenics, swimming, and health club activities (which included treadmills, ellipticals, and weights).

The bottom line: compared to a sedentary lifestyle, playing tennis extends one's life expectancy by 9.7 years. The other sports all provided benefits too, though tennis was the clear winner. Here's a summary:

• Tennis: 9.7 years gain in life expectancy
• Badminton: 6.2 years
• Soccer: 4.7 years
• Cycling: 3.7 years
• Swimming: 3.4 years
• Jogging: 3.2 years
• Calisthenics: 3.1 years
• Health club activities: 1.5 years

The authors didn't expect tennis to do so well, as you can see in this quote:

"Surprisingly, we found that tennis players had the longest expected lifetime among the 8 different sports."

For those who don't read scientific papers regularly, I should point out that the word "surprisingly" rarely gets past the editors unless the result truly is surprising. One part of the surprise is that spending more time exercising did not correlate with the greatest benefits. In fact, the cohort of people who spent the longest time on their exercise was the health club group, who showed the smallest increase in longevity.

One possible reason for tennis, badminton, and soccer doing so well is that out of the 8 sports studied, these are the ones that require 2 or more people and involve social interaction. As the authors explain,

"Belonging to a group that meets regularly promotes a sense of support, trust, and commonality, which has been shown to contribute to a sense of well-being and improved long-term health."

Or it might be that the type of exercise you get in tennis – short bursts of activity rather than slow, steady plodding exercise – might be better for you. The authors noted that

"short repeated intervals of higher intensity exercise appear to be superior to continuous moderate intensity physical activity for improving health outcomes."

If you're still skeptical, the only other study similar to this one, a very large study from Britain published last year, came to the same conclusion: racquet sports had the greatest benefit on all-cause mortality, followed by swimming and aerobics.

So if you're not doing it already, take up tennis! It's easy to find clinics and teams at almost any level (in the U.S., that is), thanks to the thousands of local clubs and to the huge network of USTA leagues, with play ranging from beginners on up, and age groups up to 85 and even 90.

That's right, there are tennis leagues for the 90-and-over set. Maybe tennis players really do live longer.

(Caveats: this was an observational study, based on surveys of people's behavior over a 25-year time span. The scientists tried to take into account all the other variables that might affect life expectancy, but humans are complicated and surveys are never entirely reliable. We don't know that tennis, badminton, and the other sports were the cause of longer life–it might be that people who play sports are generally healthier, and that both leads to longer life and allows them to play more sports.)

Can fasting help you burn off those vacation pounds?

Vacation's over, and with it comes the end of the french fries, ice cream, and other delicious but fattening foods that are hard to resist. "I'm on vacation," we tell ourselves, "I can diet later."

Well, it's later now. How about fasting? Is that an effective way to take off the weight?

Fasting has been growing in popularity in recent years. One of the latest fads is intermittent fasting, in which you fast at regular intervals and then eat all you want in between. There's the 5-2 fast, where you eat for 5 days and fast for 2, every week. Or there's alternate-day fasting, where you eat one day and fast the next, for as long as you can. Or you can fast every day for 16 hours and get all your eating done in the other 8.

Here's the thing: eating is easy, and fasting is hard. If you're going to fast to lose weight, you probably will lose a bit, but the evidence is that most people gain the weight back fairly soon once the fasting diet is over. So fasting might provide a quick reward in terms of weight loss, but the loss will be fleeting.

Suprisingly, though, fasting may be a good idea. A recent review by Stephen Anton and colleagues, in the journal Obesity, found that intermittent fasting may come with a variety of health benefits, including reducing inflammation, improving the ratio of lean tissue to fat, improving cognitive function, preventing type 2 diabetes, and possibly even prolonging life span.

How does fasting produce these benefits? Professor Valter Longo of USC, one of the leading researchers on fasting and longevity, hypothesizes that fasting forces your body to recycle many of its immune cells, particularly white blood cells. Then your body works hard to replenish its white blood cells, essentially re-setting parts of your immune system. Longo is also the inventor of the fast-mimicking diet, where you eat a special diet for 5 days every month, one that makes your body think you're fasting even though you're getting adequate calories and nutrients. (See Alice Walton's story in Forbes for more about that.)

Another effect of fasting is a change in metabolism. As Anton's article explained:

"the key mechanism responsible for many of these beneficial effects appears to be flipping the metabolic switch." 

This happens when the body runs out of its normal fuel, glucose, and begins to burn fat, which means it's converting fat to fatty acids, which in turn produce ketones. The body then uses ketones instead of glucose.

So how much fasting do you need to flip the switch from glucose to ketones? Anton et al. write that

"The metabolic switch usually occurs between 12 and 36 hours after cessation of food consumption, depending on the liver glycogen content and on the amount of exercise during the fast."

This doesn't tell the whole story, because once the switch occurs, you need to burn ketones for some time to gain any benefits. Back in 2014, I wrote about new evidence (from Valter Longo's research) that a longer fast, such as 3 days or more provide significant long-term health benefits. Three days is a long time to fast, but Longo has said that you don't need to do it more than a few times per year.

If you do decide to try a fast, don't expect it to be easy: you're going to get really hungry, and fasting can also interfere with social obligations in an inconvenient way.

I should emphasize that the evidence isn't yet clear for any of these strategies, and there are multiple studies going on now that may provide a clearer picture. Nonetheless, despite the current fad of fasting strategies and diets, fasting really does seem to have some potential health benefits.

(A final caveat: fasting can be harmful, especially for people who have other health problems. If you’re seriously thinking of trying this, you should consult your doctor first.)

Does a 3-day fast reset your immune system?

I’ve been hearing new reports lately that sound an awful lot like pseudoscience: that fasting for an extended time, two days or longer, can reset your immune system and provide other health benefits. I first heard about this when a friend and colleague at Stanford University announced he was going on a 3-day fast. To explain, he pointed to a recent study, which I’ve now read.

Diet advice, including fasting-based diets, can be found all over the Internet, and much of it is nonsense, so I was very skeptical about these latest claims.

This time, though, there might be something to it. The scientific study that my colleague told me about was published back in June by USC’s Valter Longo, who studies aging and longevity. In this paper, Longo and colleagues described remarkable metabolic changes that occurred as a result of prolonged fasting. They found that fasting for 3 days or longer–drinking only water and eating less than 200 calories per day–can truly “reset” some components of your immune system. 

The research looked at both mice and humans. (It’s far easier to run the experiments in mice, of course, but we can’t always trust that the same effects will occur in humans.) In both species, fasting lowered white blood cell counts, which in turn triggered the immune system to start producing new white blood cells. White blood cells (or lymphocytes) are a key component of your body’s immune system.

Longo’s hypothesis is that fasting (or starvation) forces your body to “recycle a lot of the immune cells that are not needed” which explains the drop in the white blood cell count. Two of the key mechanisms are an enzyme called PKA and a hormone called IGF-1, both of which are reduced by fasting. Once you start eating again, your stem cells kick back into high gear to replenish the cells that were recycled.

The human part of the study was much more limited: a group of cancer patients fasted for 1, 2, or 3 days prior to chemotherapy. The idea is that fasting might reduce the harmful side effects of chemotherapy, particularly the immunosuppression caused by some chemotherapeutic drugs. These results are very preliminary: the patients are participating in a phase I clinical trial, which is designed to assess safety, not effectiveness. Nonetheless, the results indicate that a 3-day fast (but not a 1-day fast) was beneficial for these patients.

A key finding in this research is that you have to fast for several days to get any benefit: basically, you have to fully deplete your energy reserves (in the form of glycogen), and it takes your body at least 24 hours, and probably 48 hours or more, to do this. This is much harder than a 1-day fast, which many people do routinely. 

On the other hand, Valter Longo has compared the effects of periodic fasting to long-term caloric restriction, which has been shown to prolong lifespan in mouse and other animals. In a separate review article, Longo wrote: 

“Fasting has the potential to delay aging and help prevent and treat diseases while minimizing the side effects caused by chronic dietary interventions.”

Caloric restriction is extremely difficult to achieve for humans: you have to nearly starve yourself for years. Compared to this, an occasional 3-day fast should be a snap.

Caveats: fasting can be harmful, especially for people who have other health problems. If you’re seriously thinking of trying this, you should consult your doctor first. And this preliminary evidence, though encouraging, is primarily based on mice, not people. We might eventually learn that the benefits of fasting are outweighed by other problems. Fasting for more than two days isn’t easy, either: you’re going to get really hungry. 

Does a 3-day fast truly reset your immune system? Well, maybe not a total reset, but at least a mild refresh. The science suggests that, if you can do it, a prolonged fast for 2-3 days or longer may induce your body to clean out some old immune cells and switch on production of new ones. Stay tuned.

[An interesting aside: this study was lengthy and complex, and the authors apparently went to great lengths to satisfy the peer reviewers: the paper was submitted in October 2012, re-submitted after revision in December 2013, and finally accepted in April 2014. 18 months is a very long time.]

Does a standing desk lengthen your lifespan?

Standing desks are all the rage lately. These desks allow you to stand up while working on your computer. Some standing desks can be raised and lowered, so you can alternate during the course of the day between sitting and standing. The principal argument for these desks is that they provide health benefits.

Proponents of standing desks claim, plausibly, that they give you more energy and improve posture. The CDC has found that standing desks (or “sit-stand” desks) reduce upper back and neck pain and improve moods. At Smithsonian.com, Joseph Stromberg reported that standing desks reduce the risk of obesity and type 2 diabetes. And a 2012 Australian study found that prolonged sitting increased the risk of death. In other words, standing up more and sitting less can help you live longer. All this makes me want to stand up right now.

The newest claim is that standing up lengthens your telomeres. If true, this would provide a mechanism to explain how standing up might lengthen your life. The new study, led by Swedish scientist Per Sjögren, appeared this month in the British Journal of Sports Medicine.

Telomeres are special DNA “caps” on the ends of everyone’s chromosomes. As we age, these caps gradually get shorter, and if they get too short, the cell dies. They function as a kind of molecular clock, telling a cell when it’s old. A substantial body of scientific evidence shows that if you can maintain telomere length, cells—and their owners—will live longer.

But how could merely standing more, or sitting less, shorten our telomeres? Being skeptical, I read the paper.

Here’s what Sjögren and colleagues did: several years ago, they conducted a study measuring the effect of exercise on weight, cholesterol levels, and a few other characteristics. That study included 101 people, all 68 years old. They randomly chose 49 people (14 men, 35 women) to study the effect of exercise on telomere length. They used blood samples taken 6 months apart, both before and after the exercise regimen. This was all completed back in 2011.

Previously, they reported that there was no difference in telomere length between the “exercise” group and the control group. So how can they publish a new study that seems to reach the opposite conclusion? It turns out there isn't a new study at all, but a re-analysis of the original data.

In the early study, the exercise program did have some significant effects: it increased the amount that people walked around by 1663 steps per day, and decreased their sitting time by 2 hours per day. However, people in both groups spent less time sitting over the course of the study. So the scientists re-analyzed the data and looked at telomere length as a function of four more measurements. For one of these measures, change in sitting time per day, telomere length was reduced enough that the relationship showed a p-value of 0.02.

Unfortunately for Sjögren, this new finding is based on just 12 individuals. That's a tiny number for a scientific study. And when I looked at the key figure in the paper, it’s pretty clear that the effect depends critically on just 2 of those 12 individuals who had both reduced sitting time and longer telomeres. Take those 2 people out, and the effect vanishes. The authors admitted that

“The study sample is small and we cannot rule out that the findings are a chance phenomenon.”

We've seen this sort of thing before: a small study with a minimally significant effect. Usually these types of results never get replicated. As much as I’d love to believe I could lengthen my telomeres by standing up a bit more each day, this rather implausible findnig is simply unconvincing. It’s based on a sub-group of only 12 people—and furthermore, this is a re-analysis of previous data, which feels an awful lot like cherry-picking. If there is any effect, it’s very small.

Nevertheless, other studies do show health benefits from spending more time walking and less time sitting. A daily walk probably confers the same benefit as a standing desk, but a standing desk isn’t a terrible idea either. Just don’t count on it to lengthen your telomeres.