Astronauts who return from space show stiffer arteries and insulin resistance, conditions that mimic a fast-forward version of age-related health problems here on Earth.

Researchers are monitoring how weightlessness affects astronauts in real time using ultrasound measurements one month and then five months into the flight.

So far, they've learned some of the ways the body responds to zero gravity. Since it doesn't have to work as hard, it weakens.

Canadian astronaut Robert Thirsk recalls the effects of spending six months in space.

"When I got back from space flight, the weakness, my lack of balance, my unco-ordination and the fragility of my bones, it mimicked a lot of things that I can expect as a senior citizen," Thirsk said.

"Physical activity for astronauts is important. We spend two hours each day in orbit exercising aerobically or doing muscle resistance. It doesn't stop the deterioration in our body, but it slows it down. The same lesson applies to people here on Earth as well. The geriatric population must remain physically active and stress our bodies in order to ward off the effects of aging."

Ultrasound monitoring

At the University of Waterloo, Prof. Richard Hughson leads experiments on changes in astronauts' hearts and blood vessels at the International Space Station.

"The astronauts came back from space with carotid arteries that were about 20 to 30 years stiffer equivalent than what happens with normal aging," said Hughson, who holds the Schlegel research chair in vascular aging and brain health at the university.

Increased stiffness of the arteries is associated with more heart disease and stroke.

Until now, Hughson's vascular study was limited to astronauts on just one day when they came back. Now investigators will look at their arteries while the astronauts are in space and for up to 12 months after they return.

Using remote guidance, an ultrasound technician on Earth will tell the astronauts how to move the ultrasound probe to collect the data.

The researchers will also use a glucose tolerance test in flight to measure insulin resistance, hoping to determine the mechanisms behind how those metabolic changes occur.

As space agencies prepare for longer space flights such as to Mars, Hughson said, the findings raise important questions. For instance, food and water are costly to transport to space, but astronauts need more of both when they're exercising to try to stay fit.

With files from CBC's Christine Birak