Do You Need To Worry About Vitamin D In The Summer?

Internist & Functional Medicine Clinician By Susan Blum, M.D., MPH
Internist & Functional Medicine Clinician
Susan Blum, M.D., MPH is a nationally recognized clinician, speaker, author, and teacher. She currently lives in Port Chester, New York, and received her master's in medicine from the State University of New York Health Science Center at Brooklyn and her master's in public health preventative medicine from Columbia University Mailman School of Public Health.

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Everyday someone asks me whether or not they need to take vitamin D in the summer, so I thought I'd explain why this vitamin is so important year round.

Vitamin D is much more than a vitamin. 

Every cell in your body has a receptor for D, which makes it more like a hormone than a vitamin. It supports your immune health, and is critical for people with autoimmune diseases. It's necessary for your body to absorb calcium, and women with low vitamin D levels are at a higher risk of osteoporosis. And let’s not forget about mood … many of you might notice you feel more blue in the winter when there's less sunshine.

Yes, vitamin D is made by sunshine. However, in the northern latitudes, the sun is only strong enough to stimulate vitamin D production in your skin 3 to 4 months a year, typically from May through August. During these months, your skin will make enough D to support good blood levels, if you are outside for at least 20 minutes a day, without sunscreen, typically between 10am and 2 pm, in shorts and a tank top.

In other words: your arms and legs need to be fully exposed without sunscreen during peak hours of maximum sun.

Do most people get this? No.

So if you walk or exercise outside, spend time in the garden or other outdoor activities regularly, and don’t use sunscreen every minute, you're probably OK taking the summer months off. But honestly, most of the patients I see don’t have an appreciable bump in their Vitamin D levels in the summer. They simply don’t get as much exposure as they think so they need to stay on their normal regimen. And that could be you.

While I am certainly not advocating no sunscreen, I do think it would be OK to spend 20 minutes without it, if you're trying to get your D. Then go and slather up with a broad spectrum SPF!

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Here are my suggestions: 

  1. If your vitamin D levels were in a good range before the summer (above 40) and you're outside most days during peak hours, you can probably take the summer off.
  2. If your vitamin D levels were low before the summer, or if you aren’t outside much without sunscreen during the middle of the day, you should continue your supplement.
  3. In my experience, 2000 iu/day of vitamin D is the minimum amount to maintain your levels. If you're trying to raise them, double the dose to 4000 for three months or until you're tested again.
  4. Always adjust your dose by following blood levels. Your primary care doctor can do this for you.

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