How Much Vitamin D Should I Be Taking?
What would the Neanderthals say? Some of us say none, or 600-800 IU, or 1000-2000 IU. It's a messy answer.
You would think a simple question like how much vitamin D should I be taking? would have a simple answer. But like any medical question, finding the right answer devolves quickly into a search engine nightmare of conflicting numbers, studies, unique patient considerations, and expert opinions. Answering even the most simple question becomes paralyzing, even for doctors who are supposed to know all this stuff. Then consider that vitamin D is not even an actual vitamin! It’s a hormone, really.
I’m going to present a little background in this first post, as well as some non-supplement ways to get vitamin D. The next will be about the associations between low vitamin D levels and conditions like osteoporosis, some cancers, autoimmune diseases, and infections. I will do my best to wade into the controversial, emerging consensus that despite these associations, vitamin D supplements and routine screenings with blood work are not really helping as much as we had hoped they would. Do we need to stop?
So, what is vitamin D?
First of all, it’s not really a vitamin. Vitamins are substances vital to our health and biochemistry, but that we can’t synthesize for ourselves. But we can make our own “vitamin D.” We’ve been doing that for millions of years, using a cholesterol molecule, some UVB radiation from the sun, and some modifications by the skin, liver, and kidneys to make cholecalciferol, aka vitamin D.
Cholecalciferol is a hormone. A hormone is defined as “a regulatory substance produced in an organism and transported in tissue fluids such as blood or sap to stimulate specific cells or tissues into action.” The most well known function of vitamin D is to help with the absorption of calcium from the intestines, which mineralizes and strengthens our bones. I’m going to quote an excellent long form article published in the journal Dermatoendocrinology on this subject:
1,25-dihydroxyvitamin D plays an important role in regulating calcium and phosphate metabolism for maintenance of metabolic functions and for skeletal health. Most cells and organs in the body have a vitamin D receptor and many cells and organs are able to produce 1,25-dihydroxyvitamin D. As a result 1,25-dihydroxyvitamin D influences a large number of biologic pathways which may help explain association studies relating vitamin D deficiency and living at higher latitudes with increased risk for many chronic diseases including autoimmune diseases, some cancers, cardiovascular disease, infectious disease, schizophrenia and type 2 diabetes.
What happens with classic vitamin D deficiency?
The most obvious answer is rickets. As the world industrialized many people began living in cities with tall, tightly spaced buildings. They often worked indoors, and even when outside there was a lot of pollution from burning coal. All of these factors combined to create a new problem - not enough natural sunlight exposure. Vitamin D levels dropped, and many children started developing rickets, a syndrome of weakened, decalcified bones. Here is what rickets does to the skeleton:
Scientists and doctors eventually figured out that not enough sunlight was the problem, and then discovered and isolated the hormone produced in response to UVB radiation. Vitamin D.
What other historical evidence is there of vitamin D importance?
Going back even farther, as humans and other hominids migrated out of Africa, lighter skinned individuals had an easier time manufacturing vitamin D with less direct sunlight at higher latitudes. Melanin is a great sunscreen, protecting against skin cancer and other UV radiation hazards. But too much melanin in northern climes can be dangerous for the bones and other organs that depend on Vitamin D to facilitate calcium absorption and delivery. Individuals with more melanin were at higher risk of fractures, and female pelvic bones developing a more narrow pelvic outlet - making vaginal birth difficult or dangerous. Lighter skin tones permitted more UVB to get through. More details here.
When we think of Neanderthals, we often picture this as displayed by The Smithsonian:
But in reality the Neanderthals, like those who lived in Northern Europe, have been found to carry a gene that codes for lighter complexion, and even red hair. A lighter complexion would have been favored evolutionarily because it helps to keep vitamin D production going. Many, if not most of them, may have looked more like this:
Inuits and other peoples living at extremely high latitudes were able to survive without much UV radiation at all. Even extremely light skin would not have been sufficient in polar regions to stimulate enough vitamin D. Instead their diet of seal and walrus meat, blubber, liver, and fatty fish provided them with enough dietary vitamin D to stay healthy. In this situation, vitamin D earned its reputation as a vital nutrient.
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So what is the situation in 2022?
Many of us still live in cities, or have limited sun exposure. We are warned to avoid excessive sunlight for fear of skin cancer. Justifiably so. Melanoma is the 5th most common type of cancer, and if we consider melanoma + basal cell + squamous cell carcinomas collectively, then skin cancer is actually the most common cancer of all.
If you follow the news it seems like there is an epidemic of vitamin D deficiency out there. But if we set a lower level cut off of 20 ng/ml, then the majority of the U.S. population is actually ok. Companies like Quest and Labcorp have somewhat arbitrarily set a normal value of at least 30, but as you’ll see in the next posts, this level does not really pass scientific muster.
Who is most at risk of vitamin D deficiency?
Certain populations are more at risk of Vitamin D deficiency. Breastfed infants need Vitamin D supplementation because breast milk does not have enough, and babies are not in the sun for sufficient amounts of time, especially in the winter. Elderly people’s skin makes less Vitamin D, and those in nursing homes also do not get outside enough for various reasons. And those with malabsorption disorders like Crohn’s Disease and Celiac Disease do not absorb fat soluble Vitamins like D very well. Darker skinned individuals, particularly at higher latitudes, may need to pay special attention to getting enough dietary or supplemental Vitamin D.
Should I get a lot more sun?
I think it’s important to give the dermatologists’ advice some credence in the context of this discussion. While it is tempting to try to get more vitamin D naturally by getting more sunlight, everything needs to be done in moderation. I personally do think that natural vitamin D production from the skin must have some advantages over supplementation. I think that’s one reason you will see that vitamin D supplements just aren’t giving us the results in clinical trials that we intuitively expect from them. But this is not an either/or proposition. A balance between dietary intake, some light UV exposure, and probably some supplementation is what we are trying to figure out.
I’ll let this graphic remind us about UVA, UVB, and UVC rays. It took me a long time to find a good, comprehensive one. It’s from the journal Molecules:
UVA rays make up 95% of the UV that makes it through the atmosphere and into our skin, and are around all year, all day. UVB rays are more prevalent from the spring to the fall in the northern hemisphere, and from late morning to late afternoon.
It is also hard to budget how much time one needs to be in the sun to get enough vitamin D synthesis. It depends on skin type, age, geographic location, season, time of day, altitude, air pollution, sunscreen use, and if light is passing through glass or plastic before it reaches our skin.
For example, someone with a medium skin tone might get enough sunlight to produce a day’s recommended dose of Vitamin D in just 6 minutes at noon in Miami - but even a person with the lightest skin tone could walk around all afternoon, exposed in Boston in winter, and make a trivial amount. Plus there’s the hypothermia. Union Oyster House for a warm up is excellent I’m told. I would love to warm up inside there with a beer and 6 oysters… but those 6 oysters would only give me 1 IU of Vitamin D.
What about dietary sources of vitamin D, both naturally occurring and fortified?
Think foods like certain fish, fortified dairy, mushrooms, and fortified orange juice (too much sugar though). Egg yolks have a little. Here’s a good list with approximate quantitites of Vitamin D. And below is a table I’m “sharing” from Ohio State. I went to Rutgers undergrad, and we are well known as Ohio State football’s number one rival, THE team to beat:
There is some discrepancy in terms of actual amounts in different sources, but between these two links you can get the general idea.
To wrap up this first post, vitamin D is very important for calcium regulation, and by extension bone health. Lower levels have also been associated with bone demineralization, immune system dysfunction, certain cancers, and even cardiovascular disease. I’m going to go into these more specifically in the next post, because intuitively we’ve been trying to screen and push vitamin D supplementation in the hopes that it would help. There are three major strategies for keeping our levels up - UVB exposure from sunlight, dietary consumption and fortification, and taking vitamin D supplements like pills. Over millions of years, sun exposure has been the easiest way to maintain vitamin D levels, and human skin tones differentiated most likely because of this. But as human longevity has increased, concerns about skin cancers from too much sun are very justified. I’ve linked to foods that contain vitamin D, and for that next post I’ll also run through the thorny questions of whether we should be screening everyone with blood tests, and how much if any vitamin D supplementation we should be taking.
The question How much vitamin D should I take sounds so simple, and in the office the answers have to be more simple. But with these letters I don’t want to just regurgitate some boilerplate answers for you, so thanks for coming along for the ride.