Hypertension is often called "the silent killer," because many people don't even know they have it.
And The Early Show medical correspondent Dr. Emily Senay points out that winter poses an additional, little-known threat: The cold can push blood pressure up.
Senay says, "Anybody who goes out into the cold will experience their vessels constricting. That's normal, but for people with high blood pressure, that constriction can push their blood pressure higher, into a dangerous range.
"Not only that, but the cold makes your blood stickier and thickens it, and that can lead to a heart attack. Researchers have found that big drops in temperature have led to an increase in heart attacks."
So what should people do when the mercury plunges? "It's not a matter of just bundling up, although that's good advice," Senay notes. "And certainly, we're not saying, 'If you have high blood pressure, don't go out into the cold.'
"The most important thing you need to do is control your blood pressure, and understanding some new numbers is important."
Senay continues, "The upper limit of healthy is 120 over 80. This has changed a bit, and it's still a little controversial, but this is important for people to hear. Pre-hypertension is now considered to be 120 over 80 to 139 over 89, and hypertension is 140 over 90 and above. We used to think, if we were 140 over 90, we were okay, but now we need to understand that even modest elevations within normal can confer risk as well, and the only way to know what the blood pressure is to have it checked."
How do we control blood pressure? Cut down on salt intake, Senay urges. "We are over-salted in every way, from processed food to restaurant foods."
Other ways include exercising, not smoking and limiting alcohol: "Everything we know about a healthy diet, as far as low fat. All these things are very important to control your blood pressure.
"It all sort of works together. If you get one thing under control, such as getting your weight down, that will improve your blood pressure. It will probably also improve your cholesterol.