Dr. Toshi Is In! "Vitamin D"

Dear Dr. Toshi,

People talk a lot about Vitamin D. I'm outside a lot in the sun, so I shouldn't need any vitamin D supplement, right?

You might already know that vitamin D is important in our body for the health of our bones. Vitamin D helps us absorb calcium and maintain strong bones. Without it, bones can become thin, brittle, or malformed (like rickets in children, osteoporosis in older people, for instance).

It also has other roles in our body and is involved in reducing inflammation, the health and death of cells, the function of our muscles and immune system, and glucose (blood sugar) metabolism. You may have heard that you should take extra vitamin D if you get COVID-19, but there is no specific recommendation about it from the National Institutes of Health (NIH) at this time. (The NIH says that there isn't enough data yet to recommend using vitamin D for the prevention or treatment of COVID-19. They're apparently busy doing research!)

Vitamin D is in a few foods such as some kinds of fish (e.g., trout, salmon, tuna, and mackerel), mushrooms, eggs, and there's especially a lot of vitamin D in cod liver oil. We also make active vitamin D when ultraviolet (UV) light from the sun hits our skin. Some producers even treat mushrooms with UV light to increase their level of vitamin D! Unfortunately, older people and people with dark skin don't produce as much vitamin D from sunlight.

Vitamin D is produced by UVB (Type B UV light) which can't go through glass, so indoor exposure to sunshine through a window doesn't produce vitamin D. (Besides, it's important to avoid UV radiation anyway because it increases the risk of skin cancer.)

We can also take vitamin D supplements like vitamin D2 or D3, and many foods such as milk, orange juice, yogurt, and breakfast cereals are fortified with vitamin D. In the US, infant formula is also required to be fortified with vitamin D.

Whatever the source, the vitamin D that we eat isn't the active form, so by itself it won't do any good for us. It has to be absorbed in our gut, go through our liver, and then go through our kidneys to be activated. The active form of vitamin D is called calcitriol (1,25-dihydroxyvitamin D), but it only lasts for a few hours in our body, so when we check a patient's vitamin D level, we measure the level of an inactive form of vitamin D called calcifediol (25-hydroxyvitamin D) because it stays in the body for a few weeks.

So, what's recommended as a supplement? Vitamin D2 and D3, which are inactive forms of vitamin D, are on the market but D3 raises your active vitamin D level more than D2 and lasts longer, too. So, get vitamin D3. The institute of Medicine releases the Recommended Dietary Allowance (RDA) of vitamin D in healthy people. For people between the age of 1 and 70 years old, the RDA for vitamin D is 600 International Units (IU) (which is 15 mcg) per day. For adults 71 and older, the RDA is 800 IU (20 mcg) per day. The estimated adequate intake for infants up to 12 months old is 400 IU (10 mcg) daily. For pregnant and breastfeeding mothers, 600 IU (15 mcg) per day is recommended. If you have a significant vitamin D deficiency, your doctor or provider may prescribe a much higher dose for a short period. But you can have too much vitamin D as well. Possible adverse effects of a high vitamin D level include confusion, vomiting, bone demineralization (make the bones weaker!), excessive calcium level, excessive thirst, excessive urination, and possibly even increased risk of falls among elderly people based on a recent study. Your other medical conditions may also affect what you should or shouldn't take, so please always check with your doctor or provider!

Dr. Toshiko ("Toshi") Luckow, MD, is a Family Physician at the West River Health Services Hospital and Clinics.