Vitamin D: Should you take it? Should you test for it?

Vitamin D is one of the latest in a long line of healthcare fads with a shallow foundation of evidence.  Although it might be overrated, it has its benefits and importance. 

     First of all,  you need it like you need all vitamins, although Vitamin D isn’t actually a vitamin.  On a microscopic level, our bodies are run by thousands of different, tiny machines, each which performs a single job.  They’re called enzymes and you are designed to make every single part of every enzyme except a dozen; we have to import those.  That’s  what vitamins are – imported machine parts.  Vitamin D is not a machine part; it’s a hormone.  Hormones are chemical signals that tell cells what to do. 

     Vitamin D mainly regulates your calcium balance.  It signals your intestines to absorb it and your kidneys to retain it.  Without it, your calcium ends up in the toilet.  It is therefore logical to assume that it is important for maintaining bone health.  However, this has not born out in studies.  Two large, recent studies of healthy (no osteoporosis) adults in their 50’s to 70’s did not show any significant improvement in taking Vitamin D compared to strengthening exercises alone.  However, the studies were short, 2-3 years long, so they don’t tell us anything about possible long-term benefits that Vitamin D might have.  So we’re left to guess for now. 

     There have been other studies that have shown that Vitamin D has at least a small benefit for your mood, your ability to fight upper-respiratory infections, and asthma.  There have also been some recent studies that show that it might reduce the incidence and severity of COVID-19.  However, they were very small studies, so don’t get too excited yet.  Bigger studies are underway; stay tuned. 

     Another reason Vitamin D is important is that we frequently don’t get enough of it.  Unlike the real vitamins, we do make it.  Our skin uses sunlight to start the process; the darker your skin, the harder it is.  The unfinished product is then sent to the kidneys where it’s completed.  But most of us don’t get enough sun and even when we do, we often don’t make enough of it, so we have to import some.   But the western diet is generally poor in Vitamin D, which is why we add it to milk and cereal. 

     Because of these problems and its potential benefit, it is certainly reasonable to take a daily Vitamin D supplement.  There are 400 IU (international units) in a daily multivitamin.  That’s a good start but may not be enough, depending on your lifestyle, your diet, your skin color and your kidney function.  You can take more but be careful; too much of it can be toxic.  I don’t recommend more than 2,000 IU per day unless prescribed by a doctor. 

     With all of these considerations, should you have your level checked?  The answer is: probably not unless you are at high risk or have osteoporosis.  This is where the “fad” part comes in.  The Vitamin D level is currently the fifth most common blood test being performed on older adults.  But insurance companies often won’t pay for it, and for good reason – there is no evidence that screening for, and subsequently correcting, Vitamin D deficiency makes any significant difference in people’s health.  They don’t want to pay for something for no reason, and neither should you.  To date, there are no credible guidelines that recommend it as a screening test.

     There are many practitioners out there who will order a bunch of tests and micromanage every little abnormality so that they feel, and you feel, like they are doing something.  The better doctors follow the evidence and the guidelines of the professional societies.  That means taking the long view and treating people instead of numbers.  A lot of this evidence and wisdom has been compiled by my society, the ABIM, into a website called Choosing Wisely.  You can read about the pros and cons of Vitamin D testing, and many other things, by visiting