The US Preventive Services Task Force (USPSTF) commissioned a study on whether screening for vitamin D deficiency is appropriate. Vitamin D is one of the fat soluble vitamins that has a very important role in maintaining calcium blood levels, bone metabolism & growth, and several cellular regulatory functions. Adults vary widely in their levels of vitamin D. Because of that, there is no good consensus on an optimal level. No consensus on a great lower limit to use either. That is why the USPSTF recommendation for vitamin D are unchanged from their 2014 recommendation that said the same. So if vitamin D demand depends on the individual similar to sleep or food, then maybe we should learn a little bit more about low vitamin D--and who should even care.
Testing for Vitamin D: If you ever get a lab test for vitamin D, it'll be the 25(OH)D* blood level test. Normal is anything above 20 ng/ml but abnormal varies and can be anything less than 12-20 ng/ml. Some other professional societies push normal to anything above 30 ng/ml but that may be a little extreme because that cutoff makes 40% of the US population vitamin D deficient. Let's try to test above 20 ng/ml with good nutrition and good habits.
Note: 25(OH)D is an inactive form of vitamin D formed in the liver and easy to measure. However it is not active until converted by the Kidney to 1,25 (OH)2 D or simply calcidiol.
Vitamin D Deficiency In The US Population: Depending on whether we use the 12 or 20 ng/ml as the cutoff point, we are looking at deficiency rate between 5-23%! Studies of vitamin D deficiency show correlations with increased rate of bone fractures, cancer, diabetes, heart disease, depression, and even death. That is very broad because there are a lot of other variables in play. It also shows ironically that black Americans have both lower vitamin D levels and lower rates of fractures (reported). This can be explained by looking at bone density. However, don't disregard vitamin D as it does promote higher bone density but it doesn't work alone--weight bearing exercises, good calcium intake, and being obese all contribute to higher bone density.
Treatment for Vitamin D Deficiency: Easily treated with oral vitamin D that can come in either of two forms. 1. Vitamin D3 (Cholecalciferol) or 2. Vitamin D2 (Ergocalciferol). Too much vitamin D can be TOXIC, and is typically seen with levels greater than 150 ng/ml and associated with high calcium & phosphate in the blood and calcium in the urine.
Does Treatment With Vitamin D Help? Most studies looking at vitamin D treatment for heart disease, fracture rate, and even depression found no significant different for those treated with Vitamin D versus those in the control groups and these are multi-year studies like the VITAL study which followed participants over 5 years looking at both heart disease and depression.
What these studies proved is that the addition of Vitamin D to a random group of people did not make a difference. The reason is because if you pick a random group of people, there is a 78-95% chance they would have normal Vitamin D...
So If Vitamin D supplementation is to be useful, it should be given to those who are deficient. Let's look at some of the people at risk of deficiency.
Infants less than 12 months: They are vitamin D deficient because they get very little from breast milk AND because it is recommended they should not be exposed to sunlight. The recommendation not to be exposed to sunlight is to protect from a burn but more importantly to protect their precious eyes from UV light (which we can't see, so even if it's not hot, the UV rays are still there--I was asked that before, so it's worth mentioning it). Vitamin D deficient babies develop rickets
Overweight: Being overweight is harshly stereotyped as also having an unhealthy lifestyle which is not always true. In this case however, fat cells sequester vitamin D or in other words they pull vitamin D from the blood thereby decreasing the total available amount.
Elderly: being old likely means less time outside in the sun, and sometimes a poor diet in terms of nutritional value.
Non-Hispanic Black Americans: Here the risk is due to obesity. Specifically black women are 50% more likely to be obese than white woman. On the other hand, black men are equally as likely to be obese as white men and less likely (by 10%) to be overweight compared to white men.
COVID-19: It was interesting to find that the people most likely to have low levels of vitamin D, namely the elderly, overweight, or those with darker skin would also be at higher risk of severe illness from COVID-19. Studies have been small and inconclusive, but scientists do point out to the link between vitamin D deficiency and lower immune response as well as decreased lung function. Vitamin D deficiency is also linked with increased exacerbation of autoimmune disease such as Lupus for example.
Tuberculosis in fact used to be treated with sunlight and Cod liver oil (both good sources of vitamin D) before stronger medication became available.
Foods Rich In Vitamin D: When it comes to finding foods with a high source of vitamin D, remember that the vitamin is fat soluble, so you'll find it in fatty fish like salmon, mackerel, tuna, or sardines as well as in eggs.
There is always a lot more to write about good ol' vitamin D but let's save it for another article. Final reminder--vitamin D treatment likely doesn't change outcomes if you are not deficient which is the majority of the population. If you are old, obese, pregnant, an infant, or generally love the dark and hate fish then you should consider supplementation with vitamin D.