What’s Up With Vitamin D?

Vitamin D is one of the fat-soluble vitamins, along with A, E, and K. It is also a vitamin that can result in poor health if it is deficient or in excess.  It has that J-shaped (Nike swoop-type curve) suggesting that Vitamin D levels have a goldilocks range, not too little or too much. While we know where too high or low is, we have no idea where normal lies – that ambiguity is a problem.

The United States Preventative Services Task Force (USPSTF) just reported in JAMA that 

“…the overall evidence on the benefits of screening for vitamin D deficiency is lacking. Therefore, the balance of benefits and harms of screening for vitamin D deficiency in asymptomatic adults cannot be determined.”

Let’s break their conclusion down. First, it applies to those of us who are adults, asymptomatic for Vitamin D deficiency, or who are “nonpregnant.” [1] Second, this applies to screening, meaning a Vitamin D blood test prompted by routine rather than thoughtful consideration. 

Risk factors for Vitamin D deficiency include 

• Inadequate nutritional intake – in this instance, a bigger problem for the plant-based among us, Vitamin D is found in large measure in animals and dairy products.
• Little exposure to UV B, the sun – we make Vitamin D through our skin. Darker-skinned individuals seem to have lower baseline levels than those fair-skinned.
• Obesity

But these factors account for only 20 to 30% of the variability found in Vitamin D levels. 

The problem at the bottom of the pile is that Vitamin D levels are difficult to measure, and there are a host of test procedures, all giving different results. An attempt is underway to standardize Vitamin D testing, but the majority of studies are not standardized. As a result, we have no idea what a borderline Vitamin D level might really be. In their review, the USPSFT found:

• Eight randomized control trials (RCT) showing no difference in all-cause mortality with Vitamin D treatment
• Six RCTs showing no difference in fracture outcomes 
• Five RCTs showing no difference in the incidence of diabetes
• Two trials of Vitamin D and Omega-3 (fish oil) showing no statistical difference in cardiovascular events with treatment
• Two trials showing no difference in the incidence of cancer 
• Three trials showing no difference in depression “improvement.”
• Nine trials showing no or a significant association of Vitamin D levels and falls

The enrollment in these studies used "low" Vitamin D levels that ranged from 20ng/ml to 31.2ng/ml. [2] If we consider just one source, a Vitamin D level in those ranges is deemed to be normal, you need a level of 12ng/ml to be considered deficient. My point is that without a standardized test for Vitamin D, it is impossible to determine if a Vitamin D deficiency contributes to our ill health. While these studies come with lots of numbers and statistical analysis, their underlying assumption that they have identified the Vitamin D deficientt is untrue. That makes these studies scientism, not science. 

It can’t hurt

Vitamin D can be toxic, causing a rise in your blood levels of calcium, which causes gastrointestinal discomfort, fatigue, head and muscle aches, it is an infrequent problem. The USPSTF considered 36 studies looking at treatment with Vitamin D and found little evidence that adverse effects were more common than those seen in the control or placebo arm of the studies.

The Take-away

If you are pregnant, you should be taking Vitamin D – there is science to back up that recommendation. 

If you think you are Vitamin D deficient, there is probably less harm in taking the supplement than being screened for your Vitamin D level – but understand that this is far from settled science.

If you decide to spend real money on Vitamin D, such as $320 annually for Dr. Mercola’s “special” Vitamin D, rather than $44 for a similar product available at the nearby pharmacy, maybe you should get that Vitamin D level checked. It may save you a lot of money to know that you are probably not deficient at all.   

[1] Symptoms of known diseases linked to Vitamin D deficiency include bone pain or muscle weakness – symptoms not uncommon as we age. Pregnant women require Vitamin D to prevent complications, and deficiency has long been associated with “neural tube defects” in the fetus.

[2] nanograms per milliliter

Source: Screening for Vitamin D Deficiency in Adults US Preventive Services Task Force Recommendation Statement JAMA DOI: 10.1001/jama.2021.3069