It's a New Year – 2008 and the Chinese Year of the Rat - and many people's thoughts turn to the future. For most of us, that means wishing for a long, healthy and happy life. But what can we do to increase our chances?
In almost every country in the world, the fastest growing population group is the 60 years and over age group. This has been attributed to improved health care, better housing, increased incomes and more nutritious diets. The countries in the world with the greatest life expectances include Japan, Australia, Italy, Greece and Sweden. Japan tops the longevity stakes with a life expectancy of 86 years for women and 79 years for men. The number of people living to be 100 years or more in Japan has increased greatly. In 1963, there were only 153 recorded centenarians in the country while by 2006 the figure had increased to 28,395, of which 85% were women.
While there is a genetic factor influencing life expectancy, scientist's estimate that it accounts for only about 30% of the observed differences in longevity rates. So it makes sense to look at diets and lifestyles and see what other factors play a role.
The International Union of Nutritional Sciences (IUNS) Subcommittee on Nutrition and Aging and the World Health Organization (WHO) attempted to do just that in 1987. The "Food Habits in Later Life" study looked at 818 subjects aged 70 years and over, in Sweden, Greece, Japan and Australia (the study separated the Australian group into Anglo-Celts and Greeks living in Australia). The subjects were followed for seven years. Information was gathered on dietary habits, lifestyles and general health. The study found that those with a better memory and healthier diet (particularly a "Mediterranean" type diet with an emphasis on fruits and vegetables, fish, legumes, cereals and olive oil) tended to live longer than those who didn't follow a healthy lifestyle. Not surprisingly, smoking was found to significantly shorten the life span. Several other studies in European countries have shown similar results – no smoking, moderate alcohol, and a healthy lifestyle including a Mediterranean-style diet and exercise – make for a longer and healthier life.
Why Do We Age?
The aging process is thought to be due to the accumulation of free radicals (substances formed as a result of normal body processes) which damage body tissues and DNA. In younger people, this damage is quickly and easily repaired. However, as we get older the damage accumulates resulting in chronic inflammation and irreversible DNA damage. This in turn increases the incidence of age-related conditions such as cancer and heart disease. But it appears that there are steps we can take to reduce the speed of this aging process and increase our chances of blowing out those 100 candles!
Studies conducted on rats have shown that lowering energy (calorie) intake can extend the lifespan by 30 per cent. It is thought that fewer calories results in a decrease in the production of free radicals and hence an increase in longevity. Researchers have found lower blood sugar levels, reduced insulin levels and a reduction in the production of free radicals in rats fed low calorie diets. Low calorie diets have also been shown to increase the lifespan of worms, mice and flies and an ongoing experiment in monkeys is showing positive results too.
Studies in genetics have also thrown some light on the effects of energy restriction and the aging process. A US study reported that a reduced calorie diet changed the activity of a small number of genes involved in stress response, protein repair and energy production. The activity of these genes usually decreases with age and researchers believe that a reduced calorie diet may delay this reaction and allow the genes to stay intact and active for longer.
The evidence to date in humans is indirect and most of the trials have been short term. A US study in overweight people found that those who reduced their calorie intake by 25% for 6 months had reduced fasting insulin levels and a lower body core temperature, both of which are markers associated with longevity in humans. High levels of insulin are known to increase inflammation and oxidative stress, both linked with cell damage and the aging process. In addition, weight loss is known to reduce blood pressure, blood sugar levels, blood cholesterol, the amount of body fat, heart rates and weight, all factors which in turn are linked with a reduction in the risk of a whole host of lifestyle-related disorders linked with an early demise including certain cancers and heart disease.
But what about people who are not overweight? Can they expect to live longer if they cut their energy intake? Although studies in this area are lacking, scientists have hypothesized that a lowering of insulin levels and body core temperature as well as effects on gene expression from reduced calorie diets are probably linked with an increased life span. However, caution must be exercised with consumption of a very low calorie diet. The varied risks associated with very low calorie diets include problems with nutrient inadequacy; possible loss of muscle mass and bone density; and an increased risk of anaemia, memory loss or depression. Additionally, it's not always easy to follow a calorie restricted diet for long periods of time.
The Case of the Okinawans
One of the most studied elderly populations is a group of people living on the Japanese island of Okinawa. It is believed that Okinawa has the world's largest number of centenarians (people living over 100 yrs) with 50 people per 100,000 aged over 100 yrs. In most developed countries including the USA, the rate is 10-20 per 100,000. So what do the Okinawans do that helps prolong their lives?
They appear to have "better" genes for aging which is thought to account for about one third of their longer life spans. They have a reduced risk of inflammation and autoimmune disease, which is believed to be genetically pre-determined. Yet, when Okinawans moved away from home and migrated and adopted alternative lifestyles, they did not fare as well in the longevity stakes. More recently, lifestyle changes have eroded the average lifespan in Okinawa and this implies that there are probably other factors which contributed to their longevity.
One of these is their low saturated fat diet which is high in seafood, seaweed, fruit and vegetables. The other striking factor is that their diet is low in calories, due to a cultural tradition called "hara hachi bu" meaning "eat until you are only 80% full", which is widely practiced in Okinawa. The Okinawans consume 20% fewer calories than the average Japanese diet which in turn is lower than that consumed in most other countries. In effect this means they consume about 500 cals less than the typical 2,000 plus calorie-diet consumed daily by an adult woman in a Western country.
Alcohol too is consumed in moderation and regular exercise is an important part of their lives, even when they are very old. The Okinawans are also said to have a psycho-spiritual outlook on life and use meditation and other means to reduce stress. This lifestyle seems to be paying off. In addition to their long life spans, the Okinawans have an 80% lower incidence of cancers such as breast and prostrate cancer when compared to the USA. They also have very a low incidence of heart disease and stroke. The average body mass index (BMI) is just 18-22 and they have low levels of body fat.
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