Vitamin D is so much more than just a vitamin, according to Dr. Susan Blum, a pioneer of functional medicine and author of The Immune System Recovery Plan. Every cell in your body has a receptor for vitamin D, making it more of a functional hormone than a typical vitamin. Getting the right amount is critical for immune health, hormonal health, the absorption of calcium, the prevention of autoimmune disorders, and lowering the risk of developing breast and bowel cancer. It's even associated with increased strength in young girls!

Often called the sunshine vitamin, vitamin D is produced in your body when your skin is directly exposed to ultraviolet b rays from the sun. Do you feel more blue during the winter months? Getting enough vitamin D also has a huge effect on your mood and mental cognition.

A lack of exposure to enough sunlight can cause an imbalance of serotonin and dopamine, neurotransmitters that regulate your mood. Seasonal affective disorder is a newly recognized form of depression that usually begins in the fall and affects up to 10% of the U.S population. It's critical to make sure you're getting enough vitamin D during the winter by loading up on vitamin rich foods and taking a supplement. Cod liver oil, salmon, tuna, trout, sardines, egg yolks, mushrooms, and fortified foods like cows milk, soy milk, cheese, and oatmeal are all rich in vitamin D.

Vitamin D Rich FoodsCredi Health

But what about the summer months, even with all the summer sun, are you getting enough vitamin D?

While it might sound strange to talk about vitamin D deficiency during the summer, new studies have shown that nearly half of Americans are deficient. Most people aren't getting enough direct sun exposure to keep healthy blood levels, even in the warmest months. There's also a lot of confusion about the healthiest ways to expose yourself to direct sunlight.

How much of this essential vitamin should you really be getting?

Dr. Susan Blum says, 2,000 iu a day is the minimum amount of vitamin D you should be getting to maintain your levels if they're already healthy. If you know you're deficient you can go up to 4,000 iu a day for up to 3 months to try and regulate them. The "right" amount really varies person to person though. It's important to get your blood levels tested before increasing your vitamin D consumption. Like anything else, too much vitamin D isn't a good thing either.

If your vitamin D levels were in a good range during the winter, you can most likely stop taking your supplements during the summer season. But only if you're committed to getting direct sun exposure during peak hours. To soak up enough sun for healthy blood levels during the summer you'll need to be outside, legs and arms exposed, for at least 20 minutes a day, without sun protection, between the hours of 10am-2pm. After that go ahead and slather on the sunscreen.

Studies have shown that after 20-30 minutes of sun your body reaches equilibrium. More sun exposure won't necessarily increase your vitamin D consumption. It's the consistency of daily exposure that matters long term.

What's the best way to find out if you have a vitamin D deficiency?

Ask your primary care doctor to test for it or try an online testing service. If you are deficient it can take 6-12 months to get back to healthy levels. It's also important to test every couple of months to make sure you're adjusting to your supplements, vitamin D rich foods, and sun exposure correctly. After soaking up your daily 20 minutes of sunshine protect your skin with gear and clothing that goes beyond sunscreen.