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A Deep Dive Into Vitamin D

Few supplements work, most don’t, and some are downright confusing. None will leave your head in a tailspin more than Vitamin D. It’s a hormone/vitamin that you can get from food, pills, and the sun. It boosts your immune system, helps build strong bones, and fights depression (all good things, right?) but you shouldn’t have too much of it.

Confused yet? We are. Thankfully, the National Institutes of Health Office of Dietary Supplements has a big, long article on Vitamin D that you can read here. In lieu of taking half your day to read the research, here are some of the most important points summarized:

What is Vitamin D?

Also known as Calciferol, it’s a fat-soluble vitamin (which means it gets stored in fat cells). It’s produced when UV light hits your skin. You can also eat it in food. Here are some of the highest sources of vitamin D:

  • Fatty fish (salmon, trout, tuna, sardines)
  • Mushrooms
  • Milk, including non-dairy milk (most milk products are fortified with vitamin D)
  • Fortified cereal
  • Eggs, liver, and some cheeses (cheddar)

How Much Do You Need?

Adults 19-50 need 600 IU per day. That can come from a combination of sun exposure, diet, and supplements. Most people reach their requirements through sunlight. 5-30 minutes per day is sufficient for most people, but depends on factors like sunscreen (blocks UV rays), skin melanin content (melanin blocks UV rays), pollution (blocks UV rays), and cloud cover (also blocks UV). Windows also block UV light.

Tanning beds are also effective at synthesizing vitamin D, but any form of sun exposure is dangerous for your skin. Therefore there’s a trade-off between having too much sun exposure and not enough.

Vegetarians and vegans may need more because the type of vitamin D found in plants is less usable for the body than that found in animals. In that case, supplementation might be helpful. Your doctor can tell you if your vitamin D is low using a blood test, and recommend solutions.

There are a couple of other causes of low vitamin D. The first is the kidneys taking too much out of the bloodstream. The other is the intestines not taking enough out of your food. 


There are a few types of vitamin D. The first is D2, which isn’t very effective in pill form. D3 is much more effective. Another, called 25(OH)D3 is the most effective, but not yet available in the US. It’s hard to say how much to take, but the experts caution against taking too much. Once again, your doctor can help you decide how much to take. Vitamin D isn’t flushed out of your system quickly like vitamin C, it’s possible to have too much.

Supplementing can help somewhat with things like depression, weak immune system, and weak bones (when taken with calcium). Research is still relatively inconclusive on how effective supplements are, but there are some signs of benefit.

-Coach Henry Halse



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