Obviously gardening is a physical activity. But is it really strenuous enough to constitute exercise, especially in older people?

That was the first question we asked. Charts that list calorie expenditure for a variety of activities often include gardening activities such as raking and shoveling. But those numbers are mostly interpretive. By that I mean the researchers looked at the body motions involved and then found something similar that had already been measured to determine the intensity of that particular activity. We wanted to know what’s really happening when gardeners garden. We identified nine common gardening tasks, things like digging, raking, planting, and pulling weeds. We tested older gardeners both in the lab and in their gardens, and we were able to show that gardening tasks that use upper body and lower body muscles constitute moderate intensity physical activity. By gardening 60 minutes most days of the week, these older people were definitely meeting the physical activity guidelines.

Are they getting the same health benefits associated with other forms of activity?

That’s what we’re looking at now. We’re doing a longitudinal study with a cohort of 60 older adults. We’ve taken a wide range of health measurements–physical health, psychological health, bone mineral density, resting heart rate, blood pressure, sleep quality, finger dexterity, hand strength, life satisfaction and other factors. Based on their leisure time activities, we’ve been able to determine which of the group are gardeners and which are non-gardeners. And now we’re in the process of comparing them.

What have you found so far?

We’ve only looked at data from the first year, but we’ve already seen some interesting differences. The gardeners in our group turned out to have better finger dexterity and hand strength than the non-gardeners. They also had improved self-esteem.

Why does hand strength and finger dexterity matter?

As people age, usually starting in their fifties, people begin to lose hand strength. And the loss of strength can affect their ability to do many activities. Anything that helps maintain strength is very valuable. A lot of older people develop arthritis in their hands, and we know that one of the things that helps control arthritis is continuous movement. If you continue to use your hands, the joints are going to remain more flexible and not freeze up.

I should mention that, because of our finding on hand strength and finger dexterity, we decided to test horticulture therapy in people who had experienced a stroke. Many people lose the full use of their hands after a stroke. Last summer and fall we worked with a local rehab hospital to run an intervention with stroke patients that focused on mixing soil, filling pots, taking cuttings, planting seeds, and other gardening activities that involve using hands. We haven’t analyzed the data yet, so I can’t say whether it helped. But I can tell you that the volunteers really loved it. If they hadn’t been gardening, they would have been squeezing a rubber ball to regain strength. It’s a lot easier to keep people motivated by gardening activities than squeezing a ball again and again.

Did other benefits show up in your study?

We had expected to find that gardeners had better bone mineral density, since at least one other trial has shown that, but we didn’t see a difference in our group. But then our study is still in its early stages, and most of the volunteers in our cohort are still pretty active. So some of the additional benefits of gardening may show up as we follow them over the coming years. One of the important benefits of gardening over time, we think, is that it has a lot of natural motivating factors. People really like to garden. There are tangible rewards–the sight and smell of beautiful flowers you’ve grown yourself, fruits and vegetables you can eat or share with neighbors, just the pleasure of being outdoors. Our study should eventually help us determine if gardeners are more likely than non-gardeners to stay active, and if so, if they maintain their level of physical activity over time.

Do older people adapt their gardening activities to acommodate the constraints of age–things like bad backs or bum knees?

You’d think so. But we found that older gardeners in our group didn’t. If they could no longer do something in the garden, they just didn’t do it any longer. Which is too bad. One of the things we tried to do in another program, which was purely an educational program we ran, was to encourage older gardeners to adapt. This was inspired by my dad, actually. We’ve always been a farming family. We’ve always had gardens. One year when I went home to see my parents in Michigan, I discovered that my dad hadn’t planted the garden because he sometimes couldn’t get up from kneeling. The garden was behind the barn, and he worried that if he couldn’t get up, my mom wouldn’t see him. So he just didn’t put in a garden. I told him about a nifty gardening stool you can get at Wal-Mart that you can sit on and also has armrests so you can push yourself up. The following summer he put in a garden, and I really think it helps him stay active and motivated. Little things like that can help gardeners continue to garden.

We’ve talked about older people. What about kids? With the epidemic of weight problems showing up even in pre-schoolers, is gardening a way to encourage them to be more active?

Absolutely. Kids love to garden. In fact, if you look at the natural life cycle of gardening, quite often young children love to garden. As people go through their twenties and thirties, they do very little gardening. They’re too busy getting their careers and families established. But as people move into their forties, they get back to gardening. And definitely after retirement, people who were once gardeners tend to pick it up again as a leisure time activity.

We’re in the midst of doing a study of fourth and fifth graders to see if an after-school gardening program offers benefits. We’re only in the first year of a two-year study, so we haven’t analyzed the data yet. But I can tell you that the kids love it. There’s a photo of a kid who has just picked a radish, and the smile on her face speaks volumes.

What about people who don’t have garden space of their own?

If you have a deck, it’s amazing how much gardening you can do in pots. And there are vertical garden systems that allow people to grow fruits and vegetables on walls. Another great resource is community gardens. We have one here in Manhattan, and it’s very inspiring to go there. Some of the gardeners are retired people, but others are college students who live in dorms or apartments and who always had gardens and want to do gardening again. So you have these two very distinct generations coming together, having harvest potlucks and things. It’s pretty neat.
 

© 2009 PDQhealth

Every time Dr. James H. Fowler and his colleague Dr. Nicholas A. Christakis publish a research paper, they trigger a media blitz. They grabbed headlines recently with news that obesity can spread through a network of friends almost like the common cold. If your friend—or a friend of that friend—puts on weight, you’re more likely to get chubby. If your friends and their friends are thin, odds are you will be, too. Their latest study, published in the British Medical Journal this month, shows that happiness spreads through extended social networks, as well.

First, what exactly is social network research?

For years scientists have studied how individuals make decisions. Social network research tries to elevate that up to look at the complex ways in which people interact. We’re not Robinson Crusoes, after all, living on desert islands. We’re part of complex societies, and those societies help define who we are. We’re looking at how behaviors and now emotions move through social networks.

How do you put something as complex as a social network under a microscope?

We were lucky to discover that other researchers had done some of the work for us. Since the late 1940s, scientists have been studying heart disease across generations as part of the Framingham Heart Study. As part of that study, to ensure that they’d be able to keep in touch with people, they asked participants to identify a close friend who would know how to contact them in two to four years. (It worked, by the way. Only ten people have been lost to follow up in that study, which includes more than 5,000 volunteers.) Because the study drew on people in a fairly limited geographic area, many of the friends were also participants in the Framingham study, so we had detailed information about friends of friends. The Framingham study gathered up all this great information about the social network of participants. It was the perfect study for us to do our work.

Why did you decide to look at happiness?

We’ve previously studied obesity and smoking. Those are both behaviors, of course. Both turn out to spread through social networks. So we were interested in looking to see if emotions also spread through networks. If your friends and even friends of friends are happy, is that likely to make you happy?

How did you define happiness?

We used conventional measures developed by psychologists, from a survey questionnaire that the Framingham study researchers used. Volunteers were asked how often they experience certain feelings during the previous week. Four of the items addressed happiness. “I felt hopeful about the future.” “I was happy.” “I enjoyed life.” “I felt that I was just as good as other people.” It turns out that the core disposition of happiness is quite stable over time.

And what did you discover about happiness?

We found distinct clusters of happy and unhappy people in the social network. Part of that could be explained by happy people choosing happy people as their friends. But we also found that people who are surrounded by many happy people are more likely to become happy in the future. When someone in the network became happy, friends and friends of friends were likely to become happy. It’s kind of a domino effect. Geography made a difference. People had to live within about a mile of one another to exert an influence. We think that may suggest that frequency of contact is important. It’s a lot like catching the flu. The closer your contact, the more likely you are to catch it. The same with happiness.

How far does the happy bug spread?

Surprisingly far, actually. A person is 15 percent more likely to be happy if a close contact is happy. For a friend of a friend, there’s a 9.8 percent likelihood, and for a friend of a friend of a friend the likelihood is still 5.6 percent. So we traced the effect out to three degrees of separation.

So even strangers can affect how happy people feel?

That’s right. The fascinating thing is that we found virtually the same thing for obesity and smoking. The effect goes to three degrees of separation.  In fact we’re beginning to formulate the three degrees rule.

Why three?

Our theory is that it’s a little like dropping a stone into a still pond. If you drop one stone, you’ll see waves going out across the entire pond. But if you drop several stones at the same time, the competing waves will cancel themselves out at a certain point before they reach the shore. Within an individual’s social network, there are happy and unhappy people, like those several stones. So the effect cancels itself out at three degrees of separation.

What about unhappiness? Does it also spread?

We looked at that, too. In fact, I had a bet with my co-author, Nicholas Christakis, at Harvard Medical School. He was convinced that unhappiness would spread more efficiently. His idea was that unhappiness is like fear, and for evolutionary reasons it’s a matter of survival that if someone is afraid, people around them become afraid. I put my money on happiness. I won that bet. Unhappiness does spread, our results showed, but happiness spreads more effectively. I think the reason it that happiness and positive emotions like trust are required for human beings to cooperate—to hunt large game when we were hunter-gatherers, for instance, and to build complex cities today.

What do you plan to study next?

Actually, the paper on happiness is the third of six papers we plan to publish. So we’ve looked at obesity and smoking, and now happiness. We have papers coming out in the next few months on loneliness and depression and how they spread through social networks. We’re also looking at the dynamic spread of alcoholism through social networks.

In a way, your latest findings are very reassuring, aren’t they?

I think so. They remind us that we’re all connected, in ways more complex than we sometimes think. The findings have certainly changed the way I live my life. Now I understand that my mood, my emotional state, can affect people I’ve never even met. Not just my son but my son’s friend and his friend. Not just my wife but her mother and her mother’s friends. Every day now on the way home I listen to one of my favorite songs to put myself in a good mood. I want my happiness to have a ripple effect.

Photo: Kent Horner

Q. Why is non-Hodgkin’s lymphoma of special interest to epidemiologists?

Unlike many types of cancer, non-Hodgkin’s lymphoma is on the rise, and we don’t know why. Many cancers have identifiable risk factors. But with NHL, we really don’t understand what causes the disease. Some viruses have been linked to NHL. Exposure to certain toxic chemicals has also shown a weak association. But the only recognized risk factor is abnormal regulation of the immune system. I’m interested in a possible link between circadian rhythm disruptions and cancer, so it makes sense to look at NHL to see if that might explain the disease and why the incidence is rising.

Q. What are circadian rhythm disruptions?

Almost all life on earth has adapted to alternating light and darkness, night and day. This circadian rhythm turns out to have an impact on almost every single biological pathway. Research has now identified genes that regulate circadian clocks within cells. So far, 9 human circadian genes have been identified. In the modern industrialized world, with electric light, we’re able to disrupt natural circadian rhythms–by staying up late at night and sleeping in the morning, for example. Shift work and traveling to distant time zones also disrupt circadian rhythm. The hypothesis is that these disruptions may affect cell functions and promote certain forms of cancer.

Q. What’s the evidence so far?

Several epidemiological studies have shown an association between shift work and higher risk of certain cancers, such as hormone-related breast and prostate cancer. Pilots, flight attendants, and nurses appear to be at higher risk. Our work is molecular epidemiology, which looks at genetic patterns and their association with disease risk. We’ve provided the first evidence linking a certain pattern of circadian genes to risk of NHL and breast cancer. More recently, we looked at prostate cancer. Again, we found a link between circadian gene patterns and risk of the disease.

Q. How strong is the evidence for non-Hodgkin’s lymphoma?

The evidence is preliminary because researchers are just beginning to look. A study of men working for Air Canada showed increased risk of a form of leukemia, which is a cancer of blood cells, like lymphoma. Studies have also shown that immune cells, including the cells that become cancerous in lymphoma, called B cells, follow circadian rhythms. Disruptions of those rhythms could cause cells to dysfunction. We still need to understand the mechanism. The circadian genes I mentioned are transcriptional factors. That means they don’t code for enzymes themselves but rather turn on or off other genes, which directly affect a wide range of biological processes. So disruptions in circadian rhythm could affect many functions, including cell growth. And of course cancer occurs when cells grow out of control. Interestingly, there’s evidence that inherited differences in circadian genes can even affect behavior. It’s well known that some people are morning people and others are evening people—night owls and morning larks, they’re sometimes called. That behavioral difference has been linked to a mutation in one circadian gene.

Q. What are the implications for cancer prevention?

One hope is that we will identify specific circadian gene patterns associated with an increased non-Hodgkin’s lymphoma cancer risk that could serve as a marker for the disease. Eventually we may be able to use genetic tests to identify people who are at special risk from circadian disruptions and others who can adapt to shift work and circadian disruptions with little trouble. If shift work really is hazardous to health, as a society we should try to limit it as much as possible. About 15–20% of the working population in Europe and the US is engaged in shift-work that involves nightwork. We’re also looking to see if circadian gene patterns affect a person’s response to treatment. If the molecule a drug targets is typically expressed on cells in the morning, for example, then that drug will be more effective if it’s given in the morning than at night. It’s important to remember that the link between circadian rhythm disruption and non-Hodgkin’s lymphoma is still a hypothesis. We have a lot of work to do to show if it really exists.

Q. In the mean time, should we all keep more regular hours?

That’s certainly what our work suggests. Circadian rhythm is so fundamental to biological processes that disrupting it seems to have many consequences. The invention of electric lighting and the rise of shift work could explain increases in cancer rates in many modern industrialized countries over the past century. Those changes could have a tremendous public health impact that we’re only just beginning to understand.