Just because you're not considered at risk of a heart attack or a stroke in middle age doesn't mean your lifetime risk is low, a new study confirms.

The study found that assessing a middle-aged patient's heart disease risk only five or 10 years into the future can give them a false sense of security.

"Early life decisions we make can have a significant impact on the rest of our lives -- and heart healthy choices are no different," the study's lead author Dr. Jarett Berry, an assistant professor of internal medicine at UT Southwestern Medical Center, said in a statement.

"The risk factors we develop in younger and middle ages are going to determine our heart disease risk across our lifetime."

There are a number of things that put one at risk for heart disease, but the four factors the study looked at were:

• high blood pressure
• poor cholesterol levels
• diabetes
• smoking

The researchers found that while having one or two of these risk factors might mean a low risk of heart disease in the short term, that risk can become very high in the long term.

The reason why high blood pressure for example might not raise the heart disease risk in younger adults is that heart disease is typically a disease of older age. Most people under 50 are considered low-risk.

"But most adults in the U.S. considered low-risk in the short term are actually at high risk across their remaining life span," said Berry.

He says if we want to reduce heart disease, we need to prevent the risk factors in the first place.

"What determines your heart disease risk when you are 70 or 80 is what your risk factors are when you're 40."

The study, published in the New England Journal of Medicine, is the first to look at the lifetime risk of heart disease in men and women of many races born in different decades. Previous studies have focused mostly on whites and males.

For the study, researchers tracked more than 250,000 participants in the Cardiovascular Lifetime Risk Pooling Project, over 50 years.

The four key heart disease risk factors mentioned above were measured at ages 45, 55, 65 and 75 years.

They found that people with multiple risk factors had substantially higher lifetime risks for heart disease -- as much as 10 times the rates of those without risk factors.

For example, a 45-year-old man with none of the risk factors had only a 1.4 per cent risk of having a heart attack or stroke or dying from heart disease. But having two or more risk factors hiked the risk to 49.5 per cent.

For a woman of the same age, the chance of having a heart attack or stroke in their lifetimes was just 4.1 per cent if they had no risk factors. But having two or more risk factors boosted it to 30.7 per cent.

Investigator Dr. Donald Lloyd-Jones, an associate professor of preventive medicine at Northwestern University, said it's clear that even just one risk factor significantly raises a person's lifetime risk.

"We are giving incomplete and misleading risk information if we only focus on the next 10 years of someone's life," he said in a statement.

"With even just one risk factor, the likelihood is very large that someone will develop a major cardiovascular event that will kill them or substantially diminish their quality of life or health."