Age is just a number — especially if your heart is aging faster than you are. And for many Americans, their heart is blowing out increasing numbers of birthday candles.

A recent study revealed that the average American’s cardiovascular system reflects that of an adult several years older than their chronological age. The study looked at data from a group of participants representative of about 138 million Americans ages 30 to 79 without heart disease.

American women’s hearts were on average four years older than their actual age and men’s hearts were about seven years older than their actual age.

Education levels and socioeconomic factors made a big difference in heart age. Women and men with less than a high school education, as well as those in lower income groups, showed notably higher heart ages. In fact, 24% of lower-income women and 35% of lower-income men showed a “heart age” of 10 years older than their true ages.

These results were captured by a heart age calculator that included factors like kidney function, blood pressure, cholesterol levels, diabetes status and smoking habits.

While the results of the study might be sobering, the good news is that being aware of this new information and the risk factors involved can help people make positive changes.

Small actions around your lifestyle and day-to-day habits, like quitting smoking, managing high blood pressure or improving your diet and exercise routine, can make a big difference over time.

So, though it’s not always polite to ask someone’s age, your heart might be an important exception to the rule.