People who go online to check their risk for cardiovascular disease often don't know two key numbers for assessing heart health: blood pressure and cholesterol levels, a U.K. study suggests.

Researchers analyzed data from 1.4 million visits to the National Health Service (NHS) Health Check website over the first five months after this risk assessment tool debuted online last year. (http://bit.ly/1jCWgAn)

Less than half of the visitors to this site completed enough steps to receive an assessment of their heart health, the study found. Even among people who did get an assessment, 50 percent didn't know or failed to enter their blood pressure information and 79 percent left out their total cholesterol values.

Without knowing their blood pressure or cholesterol levels, it's hard for people to get an accurate picture of their health, said lead study author Dr. Riyaz Patel of University College London.

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"For disease prevention, it's important that people take ownership of their risk and health and the first step is information," Patel said by email.

"We hope that tools like this stimulate people to think more about their cardiovascular health and then either go to a health professional to get their risk factors formally assessed or take any actions suggested to improve their health," Patel added.

Globally, 17.5 million people die from cardiovascular disease each year, accounting for about 31 percent of deaths, according to the World Health Organization. Most of these deaths are from heart attacks and strokes.

Premature heart attacks and strokes are often preventable. Lifestyle choices like getting enough exercise, eating a healthy diet and avoiding tobacco can help. Checking and controlling risk factors like high blood pressure, elevated cholesterol and high blood sugar is also important for prevention.

For the current study, researchers examined anonymous data that users entered when they did risk assessments on the NHS Health Check website from February through July of 2015.

The site calculates a "heart age" based on data users enter for basic demographics like age and gender as well as for risk factors like weight, blood pressure and cholesterol.

Compared with the user's chronological age, the heart age will be older when they have a greater risk of cardiovascular disease and younger if their risk is less than typical for their actual age.

A total of 575,782 users completed the process and provided enough information for the website to calculate a heart age.

In this subset of users, 79 percent had a heart age older than their chronological age, researchers report in BMJ Open, September 28th.

For users under 40 years old, 87 percent of males and 41 percent of females had a heart age greater than their chronological age.

In particular, 28 percent of young men had a heart age at least five years older than their actual age, the study found.

These results suggest that even among people who may be younger and not considered at the highest risk for cardiovascular disease, more screening and treatment for risk factors may be needed, the authors conclude.

The study results also highlight the need for people to get screened by doctors, so they aren't in the dark about risk factors like blood pressure and cholesterol, said Dr. Timothy Plante, a researcher at Johns Hopkins University in Baltimore who wasn't involved in the study.

"Many of the big risk factors for cardiovascular disease are related to a person's behaviors, which means that patients can reduce their risk of having a heart attack or stroke by making basic healthy lifestyle changes like quitting smoking and losing weight through diet and exercise," Plante said.

"We have many tools that estimate someone's risk of having a heart attack or stroke and patients want to use these to get an idea of how healthy they are from a cardiovascular perspective," he added. "For many patients, knowing their risk for certain diseases can be big motivators for making healthy lifestyle choices."