ANAHEIM, California - New guidelines lower the threshold for high blood pressure, adding 30 million Americans to those who have the condition, which now plagues nearly half of U.S. adults.

High pressure, which for decades has been a top reading of at least 140 or a bottom one of 90, drops to 130 over 80 in advice announced Monday by a dozen medical groups.

The guidelines, announced at an American Heart Association conference in Anaheim, mean an additional 14 percent of U.S. adults have the problem.

It's recommended that people with high blood pressure try healthier lifestyles, which get much stronger emphasis in the new advice. Poor diets, lack of exercise and other bad habits cause 90 percent of high blood pressure.

"I have no doubt there will be controversy. I'm sure there will be people saying, 'We have a hard enough time getting to 140,'" said Dr. Paul Whelton, a Tulane University physician who led the guidelines panel.

But the risk for heart disease, stroke and other problems drops as blood pressure improves, and the new advice "is more honest" about how many people have a problem, Whelton told CBS News chief medical correspondent Dr. Jon LaPook.

The upper threshold for high blood pressure has been 140 since 1993, but a major study two years ago found heart risks were much lower in people who aimed for 120. Canada and Australia lowered their cutoff to that; Europe is still at 140 but is due to revise its guidance next year.

Currently, only half of Americans with high blood pressure have it under control. Dr. Whelton said the additional patients now classified as having hypertension should be able to manage their condition with diet and lifestyle changes alone.

"Most of them just need to know they're at high risk, but they can manage that problem on their own," Whelton told LaPook.

At a health fair in New York City Monday, Adrienne Williams suddenly found herself with a new diagnosis of hypertension, her blood pressure in the 130s.

"Hypertension is considered a silent killer and now it's something I need to research, and I wouldn't have known that had I not stopped through today," Williams said.

What the changes mean
The guidelines set new categories and get rid of "prehypertension":

Normal: Under 120 over 80
Elevated: Top number 120-129 and bottom less than 80
Stage 1: Top of 130-139 or bottom of 80-89
Stage 2: Top at least 140 or bottom at least 90
That means 46 percent of U.S. adults have high pressure (stages 1 or 2) versus 32 percent under the old levels.

How common it is will roughly triple in men under 45, to 30 percent, and double in women of that age, to 19 percent.

For people over 65, the guidelines undo a controversial tweak made three years ago to relax standards and not start medicines unless the top number was over 150. Now, everyone that old should be treated if the top number is over 130 unless they're too frail or have conditions that make it unwise.

"The evidence with this is so solid, so convincing, that it's hard to argue with the targets," said Dr. Jackson Wright, a guidelines panel member from University Hospitals Cleveland Medical Center. Older people "have a 35-to-50-fold higher risk of dying of a heart attack or stroke compared to younger people."

The Associated Press contributed to this report.