The best reasons to lose weight are the obvious ones: good health and a lower risk of death and disease.

But weight loss can also improve your life in about a thousand other ways, big and small -- and a new study finds yet one more: Obese women who shed the extra pounds have higher blood levels of vitamin D.

Researchers recruited 439 overweight and obese Seattle-area women between the ages of 50 and 75 and randomly assigned them to one of four treatment groups: exercise, diet, exercise and diet, or nothing at all.

After a year, the women who lost more than 15 percent of their body weight in any group saw a leap in circulating D levels of 7.7 nanograms per milliliter (ng/mL).

What's more, researchers say the use of supplements or D-fortified foods didn't play any role here -- just the weight loss.

Women who lost fewer pounds still got a D boost -- but it was a much smaller one: Researchers say those who lost between 5 percent and 10 percent of their body weight saw an increase of 2.7 ng/mL, according to the study in the American Journal of Clinical Nutrition.

Other studies have also found that fatter people have lower D levels -- and there are several theories on why.

The simplest one is that bigger people don't go outside -- they're fat because they're sedentary. And because of their size, they're also less likely to put on a two-piece and head to the beach for some D-lifting sun exposure.

I'm not sure I buy that one -- and if you've been to the beach and seen the plus-sized sun worshippers throwing modesty to the wind, you know what I'm talking about.

Besides, even thin people are often pretty sedentary these days.

So I'll go with the more scientific theory making the rounds: Some vitamin D is locked inside your fat tissue -- and when you lose that extra weight, the nutrient is released back into the bloodstream where it can start to do the work you need it to do.

Whatever the reason, a boost of 7.7 ng/mL is a great start -- but for many people, it's not enough.

Take a high-quality D3 supplement, if you're not already... and don't be afraid to show a little skin at the beach.