The "surprising" finding has been made in a five-year study examining the health of people in NSW aged 45 and over.
The Sax Institute on Friday released its latest findings from its wide ranging research - titled "45 And Up" - which has examined the general health of the ageing population.
Professor Emily Banks says one of the most surprising findings of the state-funded research has been that diabetes can be prevented by breastfeeding.
"There are very few things you can actually do long term to prevent diabetes," she says.
"(But) women who breastfed in their 20s, 30s and early 40s, actually prevented diabetes over their lifetime.
"That to me was quite surprising."
The study of more than 250,000 people also found that life expectancy can be increased by avoiding too much sitting down.
"The longer you sit, the more likely you are going to die in the next three years," Prof Banks said.
Researchers believe standing up is beneficial to a person's health.
There have already been 50 research papers published from the study, and Prof Banks says this new information will give researchers a clear picture of positive and negative factors influencing our health as we age, such as inequalities in health services.
"I think one the challenges for Australia is to make sure that health gains are more even amongst people from different ethnic groups and aboriginal populations", she said.
NSW Health Minister Jillian Skinner praised the study group, which she said would help prevent illness in the future.
"I think it is stunning that we have this 45 and up age group that will really lead us into new areas about our lifestyle, genetic disposition, and things that are going to impact on our health", Ms Skinner told reporters.
"More importantly giving us indicators as to where we can intervene to help prevent illness and manage it in the future."
The Sax Institute is a coalition of 37 public health agencies, health service groups and universities across the state.