Walking slowly can be a sign of getting sick when old, according to a research.
Researchers found that 45-year old people who naturally walked slowly had a risk of killer diseases including dementia years before the symptoms develop.
Doctors often measure gait speed to gauge overall health, particularly in the over-65s, because it is a good indicator of muscle strength, lung function, balance, spine strength and eyesight, reports BBC.
But the researchers found they were able to predict the walking speed of 45-year-olds using the results of intelligence, language and motor skills tests from when they were three.
In this study, of 1,000 people in New Zealand - born in the 1970s - aged 45 - the walking speed test was used much earlier, on adults in mid-life.
The study participants also had physical tests, brain function tests and brain scans, and during their childhood, they had cognitive tests every couple of years.
"This study found that a slow walk is a problem sign decades before old age," said Prof Terrie E Moffitt, lead author from King's College London and Duke University in the US.
Even at the age of 45, there was a wide variation in walking speeds with the fastest moving at 2m/s at top speed (without running).
In general, their lungs, teeth and immune system were all in worse shape than people of the same age who walked faster.
The slower walkers are more likely to have older-looking brains too, the more unexpected finding that brain scans showed.
The children who grew up to be the slowest walkers (with a mean gait of 1.2m/s) had, on average, an IQ 12 points lower than those who were the fastest walkers (1.75m/s) 40 years later, reports BBC.
The international team of researchers, writing in JAMA Network Open, said the differences in health and IQ could be due to lifestyle choices or a reflection of some people having better health at the start of life.
But they suggest there are already signs in the early life of who is going to fare better in health terms in later life.
The researchers said measuring the walking speed at a younger age could be a way of testing treatments to slow human ageing.
A number of treatments, from low-calorie diets to taking the drug metformin, are currently being investigated.
It would also be an early indicator of brain and body health so people can make changes to their lifestyle while still young and healthy, the researchers said.