Leading an unhealthy lifestyle as an adult is the biggest risk factor for diabetes, British scientists say.
Unhealthy lifestyles are to blame
Childhood factors such as birth weight are no way near as important as obesity in adulthood for type 2 diabetes, the Newcastle University research shows.
Type 2 diabetes usually occurs in middle to older aged adults, but recently cases have been reported in children, probably linked to obesity.
The authors told a diabetes journal it was "never too late" to turn healthy.
Lead researcher Dr Mark Pearce said: "Obviously, it is better to eat healthily and take regular exercise from childhood onwards. But it is never too late, even if you are in your 50s.
"Our findings suggest that it is adult body fat that alters a person's risk of insulin resistance and type 2 diabetes in later life."
His study in Diabetes/Metabolism Research and Reviews followed 412 men and women from birth to age 50.
Factors such as birth weight and infant nutrition did not appear to greatly alter diabetes risk, contrary to previous reports that they might.
However, lack of physical activity and poor diet in adulthood, culminating in obesity, significantly increased the likelihood of diabetes at the age of 50.
The men and women with higher body fat and higher waist to hip ratios were more likely to have insulin resistance - an earlier warning sign of full-blown diabetes.
People with type 2 diabetes, also known as non insulin dependent diabetes, do not make enough insulin or cannot make proper use of it.
Dr Pearce said: "Previous studies have suggested that risk of poor health in later life is programmed by impaired development in the womb, and that poor growth in foetal and infant life is associated with impaired insulin secretion and sensitivity. However, not all of these studies have had access to complete data on later life.
"Our study, which has examined people from birth to adulthood, suggests that the life you lead as an adult has the biggest influence on your health, in terms of diabetes risk, in later life."
Amanda Vezey from Diabetes UK said: "We already know that lifestyle factors play a large part in the development of type 2 diabetes.
"This study further emphasises the importance of eating a healthy, balanced diet and taking part in regular physical activity."
She advised people start this as early as possible to reduce their risk.