Although the national unemployment rate hovers around 6.2%, there are large variations among the 50 states, so certain states stand out for their healthy labor markets. These exceptional states also have something else in common: They're some of the happiest states in the country, according to the 2013 Gallup-Healthways Well-Being Index.

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You may be surprised to learn that North Dakota has the nation's lowest jobless rate, at 2.8%. North Dakota has been a prime beneficiary of the shale oil and gas boom. Between that and the state's low population, it's no wonder North Dakota's unemployment rate is low. But it might also surprise you that North Dakota is also the happiest state in the U.S.

The other four states that rank in the top five by employment -- Nebraska and Utah, at 3.6% each, and South Dakota and Vermont, at 3.7% each -- are also among the happiest in America. South Dakota, and Nebraska round out the top three happiest states, while Vermont comes in at No. 6, and Utah is a respectable No. 12.

The annual Gallup-Healthways Well-Being Index is calculated through daily polls of thousands of Americans throughout the year and details how well Americans are doing in six key areas that it deems essential to physical and mental well-being:

  1. Life evaluation
  2. Emotional health
  3. Physical health
  4. Healthy behaviors
  5. Work environment
  6. Basic access

You can read about the various factors here.

While it isn't the be-all and end-all of happiness, employment plays a big role in the overall well-being of Americans, and numerous studies have found correlations between employment and various measurements of well-being.

"Life evaluation" is measured through polling, and it has been shown to be reduced by unemployment. For example, in a 2010 study titled "Dissatisfied with life, but having a good day," German academics found that although unemployed people can cope with the difficulties of joblessness and find joy in daily life, they are all around less satisfied with their lives than the employed.

Unemployment can also directly affect mental and physical health. Stress and anxiety are known to be bad for your health, and the stress and anxiety that accompany an unexpected job loss are no different. A 2009 study by Harvard researcher Kate Strully entitled "Job Loss and Health in the U.S. Labor Market" found that "losing a job because of an establishment closure increased the odds of fair or poor health by 54%, and among respondents with no preexisting health conditions, it increased the odds of a new likely health condition by 83%."

As part of the Gallup-Healthways Well-Being Index study, Gallup looked at the effects of long-term unemployment on mental and physical health. With regard to mental health, Gallup data shows that the percentage of people who report being treated for depression rises steadily as the length of unemployment rises. Ten percent of those who had been unemployed for a month reported depression. After three months of unemployment, that rate rose to roughly 15%, and after a year of unemployment, roughly 20% of respondents reported depression.

The study also shows that obesity tends to rise as the period of unemployment lengthens. Among people who had been unemployed for two weeks, 22% reported being obese. That rose to 25% after a month of unemployment, and after only three months of unemployment, 30% reported being obese.

These correlations highlight how important employment is to the overall well-being of Americans.

Foolish takeaway
Sometimes the grass really is greener on the other side of the state line. Physical and mental activity are key to happiness, so finding and maintaining a job is important. That said, there's more to the happiness equation than employment. While the states with the lowest unemployment rates are among the happiest, they all have room to improve in certain areas.

No matter how you're doing in life, always remember your biggest investment is yourself. As the Well-Being Index reminds us, it's good to remember that there's more to success in life than money and that the biggest gains and losses in life are often the result of nonfinancial choices.

Find Dan Dzombak on Twitter @DanDzombak, on his Facebook page DanDzombak, or on his blog, where he writes about investing, happiness, life, and success. The Motley Fool recommends and owns shares of Ford and Tesla Motors. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.