Interview conducted by April Cashin-Garbutt, BA Hons (Cantab) on 26th July 2012
Your recent research looked at the relationship between physical activity and life expectancy. What did you find?
With the approach of the Olympic Games, a group of researchers throughout the world thought that it would be a good time to draw the attention of the world to the health dangers of being physically inactive.
We know that physical activity has many benefits, so it is concerning that so much of the world’s population – about 1/3 – is physically inactive.
In order to try to understand how much of a problem this high prevalence of inactivity posed, we estimated the burden of disease worldwide for the major non-communicable diseases, due to inactivity.
We focussed on the diseases that the United Nations has deemed as threats to global health. These include heart disease, type 2 diabetes, and cancers – specifically breast and colon cancers, which have been linked to inactive behaviour.
We also tried to estimate how many deaths throughout the world would be prevented if every inactive person became physically active and how much longer people might live.
We found that between 6 and 10% of the diseases I mentioned are caused by physical inactivity. If we were to totally remove physically inactivity from the world, that is, if every physically inactive person became active, we would remove about 5.3 million deaths worldwide and the world would, on average, live longer by 0.68 years.
In order to understand what these numbers mean, we can compare them to statistics of a risk factor widely believed to be bad for your health – smoking. We know that smoking causes about 5 million deaths each year worldwide. Therefore, inactivity, in causing 5.3 million deaths per year, is comparable to smoking as far as health dangers are concerned.
People often ask: how much physical activity do I need to do? Many people are under the misconception that you need to be an athlete – this is simply not true. Doing the equivalent of 150 minutes a week of moderate intensity physical activity is enough. For example, you could walk briskly for 30 minutes, 5 times a week. This would be sufficient.
People also ask, what is moderate intensity physical activity? The quick gauge I like to give people is that you need to feel your heart rate going up; however, you can still carry on a conversation with a friend, but you don’t have enough breath to sing. This is a level that is moderate intensity.
You can do whatever physical activity you like that fits into this category. It could be gardening, dancing, playing with your children or grandchildren, walking the dog, swimming, cycling to work and so forth. Any of these activities do count for health.
Did you look at how different types of activity affect life expectancy?
We did not look at this as we relied on data that the WHO collects. These data are presented as a total of all physical activities, to be comparable across countries.
The WHO uses one of two standardised questionnaires to collect information on physical activity carried out during leisure time, during commuting, as part of household chores and as part of occupation, as well as walking.
These were summarised as a single measure of physical activity for the different countries throughout the world. Consequently we weren’t able to examine the effects of different types of activity.
How much physical activity should we do per week in order to make sure that our life expectancy is not shortened?
The goal is to get 150 minutes per week of moderate intensity physical activity. It is also preferable to space this activity out throughout the week, for example 30 minutes of brisk walking 5 times a week, to reduce the risk of musculoskeletal injuries.
I recommend that you do something you enjoy, as this will help you to stick to it. It is also important to incorporate physical activity into your life, for example by using a bicycle to commute or by walking to the shops. Even if you use public transport, you could consider getting off one stop earlier so that you walk the remaining distance.
So long as collectively you aim for around 30 minutes a day, 5 times per week, that is fine. For example, your 30 minutes for the day could be made up of: walking ten minutes on a morning by getting off one step earlier on the way to work, and another ten minutes on the way back; then walking for 10 minutes during lunch.
How does the lack of physical activity compare to other factors that shorten life expectancy – such as obesity?
The World Health Organisation has estimated that obesity causes around 3 million deaths a year. We know that these are estimates, but given that our estimate for physical inactivity causing around 5.3 million deaths a year, it is clear that physical inactivity is comparable to other well-established risk factors such as obesity.
How do you separate the effects of obesity and lack of exercise on life expectancy? Presumably the two are often combined?
If anything, our estimates are actually on the low end. We looked at the effect of physical inactivity on the chronic diseases we mentioned (such as heart disease, type 2 diabetes, cancers), after taking into account other risk factors like obesity, high blood pressure, blood glucose, blood cholesterol levels and so forth.
Some people say that you shouldn’t factor out these risk factors since they represent some of the pathways through which physical activity benefits health, but we wanted to be conservative. Thus, we took these other risk factors into account when we looked at the effect of physical inactivity on increasing the risk of heart disease, type 2 diabetes, and breast and colon cancers.
How does the level of physical activity vary between people in different countries?
It varies quite a bit. People in countries in South East Asia tend to be the most active and people in countries in the Eastern Mediterranean region tend to be the least active.
In the series published in the Lancet, there are data on individual countries, but we try not to focus on single countries as the assessment of physical activity was done based on self-reported responses to a questionnaire. We know that self-reported data can be imprecise, so an average across several countries tends give a more stable and precise estimate than looking at individual countries.
Is the level of physical inactivity on the rise and what do you think this means for our health systems in the future?
Worldwide, we don’t have a systematic way of assessing whether physical inactivity is on the rise. The study, in fact, is the first attempt to assess basal levels of physical inactivity in many countries worldwide.
There have been several countries, for example the US, Canada, the UK and other countries in Europe, that have systematic surveys looking at physical activity and inactivity levels over time. It appears that leisure-time physical activity probably has remained pretty much the same over the last few years.
On the other hand, occupational levels of physical activity have declined over the past few decades because there are so many technological advances. The same is true for household activities. Commuting activity levels have probably remained the same.
Thus, physical activity levels as a whole are probably stable, if not declining in high income countries. If you look at low and middle income countries that are becoming more developed, their occupational activity levels tend to go down. Commuting activity levels may also go down as people who previously had to walk or cycle to work now can afford to buy a car or a scooter. Thus, physical activity levels in low and middle income countries also likely are declining.
We took this opportunity, coinciding with the London summer Olympic Games, to highlight the dangers of physical inactivity throughout the world. We need to involve people at different levels to promote physical activity: at an individual level, a community level, state level, country level and even global level.
We need everyone working together, to get people to be more physically active. By working together, this includes providing money for places of recreation such as parks, playgrounds etc.
The analogy I like to use is smoking. The people involved with tobacco control have done such a good job working at many different levels to curb smoking. Perhaps we, in physical activity, can learn from their success.
Are you particularly worried by the level of physical inactivity in children?
The paper that I worked on looked at non-communicable diseases, which primarily occur in adults, so we did not look at the health impact of physical inactivity in children. But, another paper in the series looked at levels of physical inactivity among children and adolescents.
The figures were even more concerning. Among adolescents, only about 20% meet physical activity recommendations. Thus 80% are considered inactive.
The level of activity recommended for adolescents is a bit different from that of adults. Current guidelines ask adolescents for 1 hour of moderate to vigorous intensity physical activity per day.
How can we encourage people to be more active?
I think physical education should be emphasised more in the schools. Many schools nowadays, at least in the US, don’t focus on physical education in schools. They tend to focus on academic work.
We do know that physical activity is associated with improved test scores in children. Thus, it is important for children to have periods when they are physically active.
Are there any plans that are going to be put in place to achieve this?
There has been a large body of research looking at what physical activity promotion programs work. There are several that do work.
For example, we know that mass media campaigns on a large scale work. We know that social support networks such as buddy systems and walking clubs help people be active. We do know that environmental factors are also important. For example, it is important to have a safe place to walk, such as a park. Shaping policies for community and neighbourhood design, land use (e.g., increasing green space), and travel choice (improving public transport) can increase physical activity.
One problem with mass campaigns is that they tend to be one-off events. We need to try many initiatives on a more continuing basis to encourage people to be active.
How do you think the future of physical activity is going to progress?
If you get up in a morning you don’t question whether you are going to brush your teeth – you do it automatically. I am hoping that we will all work together to achieve a situation so that we don’t even question whether we should be physically active – we are simply physically active as part of our daily lives.
What are your plans for further research into this field?
I am hoping that this series on physical activity draws people’s attention to the fact that physical activity is very important for health. Often it is overlooked, either in terms of policy or funding for research.
I am hoping that this work will draw the attention of many organisations throughout the world, including researchers who want to look at the health effects of physical inactivity, as well as those looking at how physical activity can be promoted throughout the world.
Do you have any further comments?
One thing I want to emphasise is that while 150 minutes of physical activity per week is the goal for adults, it is important to realise that the relation between physical activity and health is not an “all-or-nothing phenomenon”. By this I mean that as far as health benefits are concerned, you are better off doing any amount of physical activity than none at all. And of course more is better than a little.
For anyone who is worried that they cannot reach the 150 minutes per week, I would recommend just doing what they can – 10-15 minutes a day is better than doing nothing.
Where can readers find more information?
They can find our paper here: http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(12)61031-9/abstract
About Dr I-Min Lee
Dr. I-Min Lee is Professor of Medicine at Harvard Medical School and Professor of Epidemiology at the Harvard School of Public Health.
She received her medical degree from the National University of Singapore, a Masters degree in public health and a Doctoral degree in epidemiology, both from the Harvard School of Public Health.
Her research primarily focuses on the role of physical activity in preventing chronic diseases and enhancing longevity, and in women’s health.
Personality traits influence physical activity and sedentary behavior