These are the darkest days of the year. The sun is low in the sky, and we tend to see long stretches of cloudy, rainy, dreary days, and it can have an impact on our health.

Vitamin D is important to our health for many reasons, mainly because it helps our body absorb calcium, which is good for our bones. Our bodies absorb vitamin D through our skin via direct sunlight. These days, we don't get nearly as much sunlight compared to other times of the year. Twenty to 30 minutes of sunlight a few times a week is all we need to keep a healthy level of vitamin D.

We measure sunlight, or solar irradiance, with a pyranometer. There's one on top of the Atmospheric Sciences building at the University of Washington. Here's a stark example: back on June 19, a day with nearly 16 hours of daylight and full sunshine, that pyranometer measured about 25 MegaJoules (a unit of energy) of solar irradiance. That's a lot.

Now, compare that to what we saw just last week, November 26, which was a really cloudy, rainy day. On that day we measured a measly 0.75 MegaJoules. That's 3 percent of the solar energy we got on that summer day!

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Here are some tips to make sure you're getting enough vitamin D:

Get outside during the middle of the day

Even if it's cloudy, you can still absorb some vitamin D. A walk outside when the day is at its brightest can also boost your mood.

Drive up into the mountains

This is mainly true during days with temperatures inversions and fog in the lowlands. A temperature inversion is when the temperature rises as you get higher in the sky. Typically, the atmosphere cools the higher up you go.

Sometimes, it can be a lot sunnier aloft. Not to mention the snow reflects sunlight back onto you.

Take a supplement

Try supplemental vitamin D pills or drink milk fortified in vitamin D.

Drive to the rain shadow

Head to the lee (downwind) of the mountains where downslope wind can create some clearing. This can be found northeast of the Olympics near Sequim when strong southwest wind is present. Also, after a front passes, it tends to clear east of the Cascades.

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A rain shadow northeast of the Olympic mountains.

Fly to a sunnier climate

Yuma, Arizona; Los Angeles, California; and Miami, Florida round out the top three sunniest cities in the U.S.

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Arizona.