Dear Nutritionist: I’ve heard that most people who live in the Pacific Northwest don’t get enough Vitamin D. Do I still need to take Vitamin D in the summer?

Dear Member: Vitamin D helps in the production of serotonin, a neurotransmitter that can help you feel calm, relaxed, and happy. Vitamin D deficiency is associated with low mood, and it’s also associated with PMS, seasonal affective disorder, mood disorders, and depression.

While we do get Vitamin D from the sun, it can be hard for those of us who live in the Pacific Northwest to get enough sun to maintain our Vitamin D stores. Wearing clothing that covers our skin and wearing sunscreen (which you should do!) prevents Vitamin D from being synthesized. The only way to tell if you have adequate Vitamin D stores is to get a blood test. Most labs use a reference range of about 20 – 55 ng/ml for Vitamin D levels. Research suggests that levels for optimal health are much higher, about 50 – 80 ng/ml.

While the recommended daily allowance for Vitamin D has been set at 600 IU, most studies suggest that you need at least 1,000 to 2,000 IU a day. The upper limit is 4,000 to 10,000 IU a day. If you take a supplement, make sure you take vitamin D3 (cholecalciferol), which is the active form of Vitamin D. Talk to your doctor about what level is right for you.