Vitamin D3, or “the sunshine vitamin,” has been a hot topic in the health world for a while now. Tired? You might blame your D levels. Feeling a little blue? Must need to get some sun (and D).

Some research out there suggests testing vitamin D levels is superfluous and not necessary for most people — especially because many experts don’t agree on what constitutes as a vitamin D deficiency. It may not be worth it to get your vitamin D levels measured, but it couldn’t hurt to take 1000 IU a day or drink a fortified glass of skim milk. You just want to make sure you aren’t low in this essential vitamin, as many studies point to vitamin D as helpful in preventing diseases like cancer.

In fact, a recent one published in BMJ analyzed Danish government health records of 95,766 people, and discovered that those with a genetic variant that causes low vitamin D levels had over a 40 percent increased risk of dying from cancer. In fact, they had a 30% increased risk of death from any cause, compared to those without the genetically low D levels. (For the nutrition wonks out there: Three is the active component — D2 is what is commonly measured, and taking a supplement that is 2 or 3 seems to be subject of an unresolved debate about which is most effective. So when you see vitamin D, just assume it is the active component we are talking about.)

Vitamin D is essential for bone strength and increases collagen production, which means less wrinkles and younger-looking skin. Another positive reason to keep your levels high? Getting too little sunlight, and therefore, having low D levels, has been associated with depression. And new research from University of Georgia found a strong link between D deficiency and seasonal affective disorder (SAD) a type of seasonal depression that occurs in the winter when sunlight is at a minimum and the sky tends to be dark and gloomy— causing your mood to follow suit. Vitamin D3 is important for producing feel-good chemicals serotonin and dopamine in the brain. Low levels of both are linked to depression, making a strong case for vitamin D’s role in helping regulate mood.

Few foods actually contain vitamin D naturally, but some products tend to be fortified, meaning D is added. Here are a few good suggestions for vitamin D-rich foods to add to your diet to help keep your levels up:

  • Milk — almond, soy or cow’s (choose skim, and make sure your choice is fortified with D)
  • Orange juice fortified with D (check labels) — get it with the pulp so it doesn’t raise your blood sugar levels too much.
  • Breakfast cereals fortified with D (check labels)
  • Salmon
  • Plain, fat-free, no sugar added yogurt
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