Vitamin D is an essential molecule, which means we need to get it from outside our body. Vitamin D plays an important role in immune function, bone health, neurologic and cardiac function.
Most of us know that one pathway for getting the vitamin D we need is through our skin when we're exposed to the sun. However, with good sun-blocking (important) and because the Northwest is well above the 35th parallel, most of the time we can't count on the sun to get us all the D we need.
So we turn to diet. We can get additional vitamin D from dietary sources, but unfortunately it is in pretty small quantities in most food: Fatty fish has the most, about 200 IU of vitamin D per ounce; an egg has about 50 IU; 8 ounces of milk has about 100 IU. To get to the recommended allowances would require regularly consuming considerable amounts of fish, eggs and milk every day.
That leaves supplements as the last option for staying topped up with vitamin D. There are drops, gummies, chewables, tablets and capsules. They can be found online, at any pharmacy or grocery, and at Costco. So, how much is enough?
That's where it gets a little complicated. The Institute of Medicine recommends 400 IU per day of vitamin D from birth to 12 months of age, 600 IU per day from one year until age 70, when it increases to 800 IU per day. However, those values can be considered a daily minimum amount. The IOM committee also gives a daily "upper level intake." That dose is considerably more: 4,000 IU per day for adults; 3,000 IU per day for kids ages 4 to 8; 2,500 IU per day for kids ages 1 to 3; 1,500 IU per day for infants ages 6 to 12 months; and 1,000 IU per day for infants up to 6 months old.
Meanwhile, the Endocrine Society suggests adults may need 2,000 IU daily to maintain satisfactory levels; for children and adolescents the recommendation is 1,000 IU daily.
I extrapolate from these recommendations to suggest it seems reasonable that infants from birth to 12 months get 600 IU per day, increasing to 1,000 IU per day from 12 months to school age, bumping up again to 1,500 IU per day for school age kids, and finally reaching 2,000 IU per day for adolescents and adults.
In practical terms, there are a few considerations to keep in mind. While lactating mothers do transfer some vitamin D through their breast milk, vitamin D is a big molecule, so it does not get through in as great a quantity as would be preferred, especially if the mom is deficient to start with. So breastfed infants should get a daily supplement. And, incidentally, while we are discussing this age and supplements, it is recommended that infants who are exclusively breastfed receive some supplemental iron starting at about 4 months of age, either through fortified baby cereal given daily, or with a supplement, at least until they are consuming regular iron-rich foods like meats, beans, greens and legumes.
After age 12 months, kids, adolescents and adults should get 1,000 IU to 2,000 IU per day on average all school year.
There is a caveat: This is a fat-soluble vitamin, so fat cells need to be repleted before serum levels begin to rise. For this reason, it is common for individuals with more abundant adipose cells to require much higher doses than those suggested above, but this should be done with the guidance of a care provider, likely using lab levels as a guide.
The vitamin D situation is a good example of how our modern lives do not always reflect that for the bulk of humanity's history most of our ancestors lived closer to the equator. So, for those of us who are the progeny of migrators, we'll need to tweak things a bit to accommodate our modern realities.
Matt Thompson is a pediatrician at Spokane's Kids Clinic.