It’s that time of year again. Many of us wake up and go to work in the dark. We work all day and return home in the dark. With the days getting shorter and the weather turning cold, we turn our attention to vitamin D supplementation in the feature article of this month’s newsletter. Questions I typically field from patients range from: do I need to be concerned about getting enough? How much do I need? And who in particular is at risk of deficiency?
First, let us establish that vitamin D is not an essential nutrient, classically defined as any substance that we must consume in our diet because we cannot make it adequately on our own. Our skin can make vitamin D from ultraviolet B (UVB) radiation in sunlight. In fact, very few foods even contain vitamin D naturally. Fish liver, mushrooms, certain types of fish and a few other foods contain some vitamin D. Cow’s milk has been artificially supplemented with vitamin D. So you see, from a natural perspective this shouldn’t even be a nutritional issue at all. Yet we often do consider this a nutritional issue because if you don’t get enough from sun exposure, you can eat vitamin D and absorb it through your gastrointestinal tract.
Vitamin D has recently become scientifically popular because vitamin D deficiency has been linked to cancers, multiple sclerosis, frailty, falls, and many other ailments. Yet for all the interest, there have not been consistent results that show that supplementing with vitamin D in a pill actually does anything useful for chronic diseases. Vitamin D has been shown in some studies to slightly reduce the risk of falls, especially in deficient people (for example, institutionalized older adults).
Getting enough vitamin D from the sun is easy to do in the spring, summer, and fall, no matter how far north you live. Factors that make a difference in how much vitamin D you make include skin color (the darker your skin color the less you make), time of day, length of day, and skin covering, including sunblock1. If you have exposure to the midday sun (between 10 a.m. to 3 p.m.) for 5-30 minutes twice a week on the arms and legs you would get sufficient vitamin D. For pale skin you might need as little as five minutes, and for dark skin you might require at least 30 minutes. It’s important to note that you can make vitamin D even on cloudy days. Clouds, shade, and severe pollution/smog clouds reduce vitamin D synthesis by about 50-60% yet you’ll still be making vitamin D. Windows block UVB radiation but not all of the ‘tanning’ radiation, UV A, so you won’t make any vitamin D driving in a car unless the windows are down. Sunblock of any SPF strong enough to stop a sunburn will stop almost entirely all vitamin D synthesis on the skin to which it is applied.
Severe vitamin D deficiency causes rickets and osteomalacia, which are problems with bone mineralization resulting from inadequate calcium and phosphorus. Vitamin D helps with calcium absorption in the intestine. Very low vitamin D causes very low calcium absorption, which triggers other changes including low phosphorus and hormone system changes. Rickets and osteomalacia are uncommon but they are very real risks for certain populations. Populations at risk are included in Table 1.
Populations at risk of vitamin D deficiency (darker skin pigment increases risk across all groups)
People who should be concerned about possible vitamin D insufficiency include institutionalized people, people living in the northern US or at higher latitudes who have long winters, and exclusively breastfed infants and their mothers. Exclusively breastfed infants should take vitamin D, at a level of 400 IU/day. This can be administered as a droplet placed in the baby’s mouth. Those individuals over the age of nine who fall into these categories should take 600 IU of vitamin D a day while elderly institutionalized people should take 800 IU per day. Keep in mind that more is not better. It is possible to have too much vitamin D. The maximum adult dose is 4000 IU per day, and it is significantly lower for children.
You may now be wondering how often your doctor should check your levels. While I haven’t seen any recommendations based on unequivocal scientific evidence, I can offer the following as a general guideline reflecting my approach. In my hometown of Rochester, NY, I will certainly check vitamin D levels on those individuals with calcium, bone or parathyroid hormone problems and will also often screen those people in the categories from Table 1 as well as pregnant or breastfeeding women. For those not in a higher risk category, I do not suggest routine vitamin D screening. I simply encourage everyone to get as much outdoor time as possible while strictly avoiding any sunburn, along with weight bearing exercise for good bone health.
As with all information that’s shared in our monthly newsletter, this is a good topic to discus with your personal doctor. As winter settles in, I recommend a vitamin D supplement of 600IU a day for adolescents and adults. This should hold us over until that next glorious spring with its promise of warmer weather, longer days, and outdoor fun. Until then, I recommend as much outdoor activity as possible: walking your dog, cross country and downhill skiing, hiking, ice skating at an outdoor location, snowshoeing, or more traditional activities like golf, tennis and biking in the less snowy areas of the country. The idea is to have fun and stay active and fit while keeping your vitamin D levels sufficient.
Copyright 2023 Center for Nutrition Studies. All rights reserved.