Nutrition
Death is inevitable, but research shows that eating plenty of fruit and vegetables may help extend your stay.
Death is inevitable, but research shows that eating plenty of fruit and vegetables may help extend your stay.
Question:
The recent column about asparagus ( Nutrition, October 19) said that a British study found “a higher intake of fruit and vegetables was linked to a lower risk of all-cause mortality”. And that “each additional serving of fruit and vegetables a day reduced mortality risk by about 5%”. How can that be, as we all have 100% risk of mortality? If a dietary change of any sort reduces the chances of dying of cardiovascular disease, it must therefore increase your chances of dying of something else.
Answer:
You’re quite right. The lifetime risk of dying is one per person, or 100%, points out Rod Jackson, a professor of epidemiology at the University of Auckland. But we do have the opportunity, through lifestyle and other modifiable factors, to extend our expiry date and enjoy a few more healthful years. That’s where fruit and vegetables come in handy. To explain, the 2014 British study you mentioned was a major review and meta-analysis that collected and combined data from 16 studies. It looked at how many servings of fruit and vegetables the participants were eating each day, along with deaths and causes of death of the participants during the study period.
The 16 studies covered vastly different timespans – from 4.6 to 26 years. In all, there were 56,423 deaths (11,512 from cardiovascu
lar disease and 16,817 from cancer) among the 833,234 participants.
To work out if eating fruit and vegetables was associated with mortality risk or, specifically, deaths from cardiovascular disease or cancer, statisticians use a range of calculations, including the hazard ratio, says Jackson.
Hazard ratio is a measure of an effect of an intervention on an outcome over time. In this case, the
intervention is fruit and vegetable intake. We want to see what happens to deaths (the outcome) when we vary how much of these we eat.
So, the statisticians would have pooled the results from all the studies.
They then calculate how many deaths occurred in each consumption category each year. That is, how many deaths occurred each year in the group of people who consumed one serving of fruit and vegetables a day and how many deaths occurred each year among those who consumed two servings, and so on.
For simplicity’s sake, let’s say there was a rate of 100 deaths per 10,000 people in one year among those who ate one serving of fruit and vegetables a day, and a rate of 95 deaths per 10,000 people in one year among those who ate two servings a day. The hazard ratio of two servings versus one serving would be 95 divided by 100, which equals 0.95.
In this case, the statistician would say the pooled hazard ratio of consuming two versus one serving of fruit and vegetables is 0.95. So, “every additional serving of fruit and vegetables a day was associated with a 5% lower risk of all-cause mortality. I got the 5% by using the following calculation: (1.0-0.95) x 100 = 5%,” says Jackson.
In the British study, they analysed variations of fruit and vegetable intake and death rates and found that each extra serving of fruit and vegetables was associated with a 5% lower risk of all-cause mortality (per year), with the effect flattening off at about five servings a day.
So, there were fewer deaths in each study year among people who ate more fruit and vegetables, which suggests that if they’re not dying, they’re living longer.
In other words – eating more fruit and vegetables is associated with greater longevity.
Will they die of something, some day? Yes, of course, with 100% certainty. They may still die of cancer or cardiovascular disease one day, too. But, statistically, they’re more likely to live a longer life before they die of something than those people who eat fewer fruits and vegetables.
There were fewer deaths in each study year among people who ate more fruit and vegetables.