Millions upon millions of Americans are stressing out.

Forty percent of the nation’s workers say they experience stress on a daily basis, according to a Gallup Poll from June. That number climbs to 50 percent among the unemployed. And the problem seems to be getting worse. Forty-eight percent of U.S. adults believe the stress in their lives has escalated during the past half-decade, says the American Psychological Association.

Several factors contribute to the daily pressure that Americans feel, ranging from unemployment and shaky personal finances to traffic, crime, and pollution. The intensity of this toxic mixture varies from market to market across the country, as does the level of stress.

Nowhere is the situation worse than in Detroit, which ranks as the most stressful metropolitan area in America, according to a new study by Portfolio.com and bizjournals.

Detroit is burdened with a hefty unemployment rate, 14.3 percent at midyear, the third-worst figure in the nation’s 50 largest markets. It’s also among the 10 places with the most murders, the most robberies, the most heart attacks, the most families in poverty, and the fewest sunny days.

The result, to Detroit’s misfortune, is America’s ultimate recipe for stress.

Portfolio.com and bizjournals created a 10-part formula to estimate the stress levels in the nation’s 50 biggest metros, using the latest data available from several government agencies and private firms. (To get details on the methodology used to construct this study, click here.)

The runner-up on the stress index is Los Angeles, which is saddled with the most expensive housing and second-worst air pollution among the 50 biggest metros. It’s also afflicted with an unemployment rate of 11.6 percent.

Rounding out the list of America’s 10 most stressful markets are Cleveland, California’s Riverside metro, St. Louis, New York City, New Orleans, Chicago, Birmingham, and Miami-Fort Lauderdale.

Life is considerably calmer in Salt Lake City, which ranks as the nation’s least-stressful metropolitan area.

Salt Lake City has the lowest murder rate of any major metro, 94 percent smaller than Detroit’s. It also ranks among America’s four best markets for short commutes, low unemployment, and low incidence of circulatory-system diseases.

Virginia Beach-Norfolk holds second place on the low-stress list. It enjoys the strongest pace of income growth in any of the 50 biggest metros, as well as the smallest robbery rate.

Other markets with low levels of stress, ranking from third through 10th place, are Minneapolis-St. Paul, Raleigh, Austin, Oklahoma City, Denver, San Antonio, Kansas City, and Phoenix.

(To see how the nation’s 50 largest metropolitan areas ranked on the stress test, download a pdf by clicking here.)

Portfolio.com and bizjournals analyzed a broad range of factors to pinpoint the metros that subject their residents to unusually high or low amounts of stress. The following are the 10 indicators included in the study, along with a brief summary of the worst and best markets.

—Unemployment: The recession has taken a toll all across the country, leaving 20 of the 50 biggest metros with double-digit unemployment. Las Vegas is the worst at 14.5 percent, followed by Riverside at 14.4 percent, based on midyear data from the U.S. Bureau of Labor Statistics. Washington, with 6.4 percent unemployment, fares the best.

—Income growth: Income levels dropped in 47 of the 50 markets between 2008 and 2009, says the U.S. Bureau of Economic Analysis. The worst drops belong to Las Vegas, Charlotte, and San Jose. Who are the three fortunate gainers? Virginia Beach, Pittsburgh, and Baltimore.

—Poverty: Memphis has the worst poverty problem in the study group, with 13.9 percent of its families officially classified as poor by the U.S. Census Bureau. San Antonio and Houston are next on the poverty scale. Washington, on the other hand, has the lowest metropolitan poverty rate, 4.7 percent.

—Deaths from circulatory-system diseases: New Orleans has the highest number of deaths caused by heart failure, hypertension, and stroke, a rate of 414.4 per 100,000 residents, based on Centers for Disease Control records for 2006. Pittsburgh and Cleveland are almost as bad. The lowest rates belong to Austin, Raleigh, and Salt Lake City.

—Sunshine: Pittsburgh is the gloomiest market, attracting only 45 percent of possible sunshine in a typical year, according to the National Climatic Data Center. Seattle, Buffalo, and Portland, Oregon, are nearly as dark. The sunniest metros are Las Vegas and Phoenix at 85 percent.

—Unhealthy air: A sweep for California. Sacramento, Los Angeles, and Riverside suffer the worst ozone problems in the study group, as measured in 2008 by the U.S. Environmental Protection Agency. Another California metro, San Francisco, has the smallest ozone level, followed by Minneapolis-St. Paul and Portland.

—Robberies: Cleveland has the worst rate, 827.5 robberies per 100,000 residents, based on central-city records compiled in 2009 by the Federal Bureau of Investigation. St. Louis and Cincinnati are the next worst, while Virginia Beach has the lowest robbery rate, 103.6 per 100,000.

—Murders: New Orleans is the deadliest city on the list, with 51.7 murders per 100,000 residents in 2009. St. Louis and Detroit are the runners-up. The safest city is Salt Lake City, with 2.2 murders per 100,000. The rates in Austin and San Jose are nearly as low.

—Commuting: Traffic is a grind in the New York City area, where the typical commute to work takes 34.55 minutes, according to the U.S. Census Bureau. Washington and Chicago also have serious congestion. Roads run free and easy in Buffalo (20.78 minutes) and Oklahoma City (21.35).

—Housing costs: Affordability is based on a comparison of median home values and median household incomes, as reported by the U.S. Census Bureau. Three California markets (Los Angeles, San Francisco, and San Jose) have the worst ratios, while Buffalo, San Antonio, and Pittsburgh enjoy the most affordable housing.

To download a PDF that shows how the nation’s 50 largest metropolitan areas rank according to our stress test, click here.