HONG KONG (Reuters) - A study in Australia has shown that changes occur in blood vessels in the eyes of heavier and obese children from as young as six, warning signs that might be linked to cardiovascular disease in later life.

Previously, these changes -- widening of veins and narrowing of arteries -- were only observed in the retinas of heavy teenagers and adults, and this is the first time that such troubling signs have been seen in children so young.

Writing in the International Journal of Obesity, the researchers called for extensive monitoring of these subtle blood vessel changes as they can be an early indication of risks such as hypertension and stroke when the children enter adulthood.

“It was initially thought that the risk profile developed in adolescents and young adults, but (this study) suggests that these changes probably occur even at an early age,” Paul Mitchell, a professor at the University of Sydney’s Centre for Vision Research, said in a telephone interview.

“It may be worthwhile examining children or adolescents for subtle retinal vessel size as these could be markers of a person’s risks as they get older into adulthood.”

The retina is a thin layer of neural cells that lines the back of the eyeball.

The study involved 1,740 six-year-olds from 34 schools in Sydney.

After accounting for differences such as sex, ethnicity, length of the eyeball, birth weight and mean blood pressure, the researchers found unique changes in minute blood vessels in the retinas of children who were over the mean weight.

The average diameter of their retinal veins was 2.1 microns larger than those of their lighter peers. However, the average diameter of retinal arteries in the heavy children was 2.2 microns narrower than other children.

Veins carry low-oxygen blood back to the heart, while arteries carry oxygenated blood from the heart.

“The reason for widening of the veins may simply relate to a larger blood volume associated with a heavier child. It’s harder to explain the effects on the retinal (arteries). It could be a reflex response in obese children, but that remains to be seen,” Mitchell added.

It also remained to be seen if the changes to blood vessels were reversible.

“In adult populations, we haven’t (seen) reversibility so often. For the narrowing of arteries associated with elevated blood pressure, even when blood pressure is back to normal, the arteries don’t seem to respond, but we don’t know about the (retinal blood vessels),” Mitchell said.