Dr. Vicki: Vitamin D, the Sunshine Vitamin

By Victoria Rhoades, ND

What is it? Vitamin D is a steroid-based vitamin – that means the chemical structure resembles cholesterol. There are several specific forms of the vitamin; ergocaliciferol (D2) and cholecalciferol (D3) are the two most important to human health. Plants make vitamin D2; humans make D3 when the skin is exposed to UV-B rays from sunlight. Foods can be fortified with either one.

Natural food sources include fish (cod liver oil contains a fair amount, although it varies from brand to brand – read the label), mushrooms, and meats. Foods fortified with vitamin D include milk and cereals.

Furthermore, some small chemical modifications naturally occur in the body to convert from the source vitamin D, into the activated forms. This is a two step process, occurring first in the liver, and then in the kidney. Both steps are needed. Thus, kidney and liver health are both important to consider; vitamin D levels may be low if one of these organs is not working properly. Further, the speed of the kidney step can be affected by estrogen, insulin, cortisol, and other hormones.

Why do we need it? The main function of vitamin D in humans is to maintain normal levels of calcium and phosphorus in the blood. It also helps with absorption of calcium from foods, and it’s been tied in studies to prevention of osteoporosis and osteomalacia. There is some evidence that it can be useful in maintaining a balanced and strong immune system, including helping to prevent cancer; it may also help high blood pressure and help with better control over asthma 1. Scientists and doctors are still gathering evidence on vitamin D.

How do I know if I need to take it? The best thing to do is to get your serum vitamin D levels checked – the spring is best, since after a long cool winter, your levels will be at their lowest ebb and the doctor will have a better idea of whether or not supplements are right for you. This year, that would be about now, after our rather cool, wet spring. Note: most people living above the latitude of San Diego have lower than optimal levels – even in the summertime.

Getting a blood test is easy – your doctor can order one for you at any lab. It’s important to note the units on your result when interpreting your levels: some labs report in “nanograms per milliliter” and some report in “nanograms per kilogram”. When you get your results, make sure you are looking at the right units. Normal levels are as follows (per the NIH2):

And what about sunlight? Well, you could be getting your daily dose from light exposure, except for two things. Number one, we just don’t get much sun for several months of the year here, and the angle of winter sunlight is such that it reduces the ultraviolet light waves needed to make Vitamin D. Do you really want to go outside wearing shorts and a t-shirt when it’s 40 degrees outside? I don’t suggest it! Number two, by the time it warms up (July 5th, most years), you might be tempted to “catch up” and stay outside for a couple of hours every day, and thus increase your risk of skin cancer. Sun block may prevent the ultraviolet light (UV-B) from getting to your skin. You can get some vitamin D this way, but probably not enough. That leaves eating Vitamin D rich foods (wild salmon anyone?), and possibly also taking a supplement.

But wait! There’s more! There is an ongoing debate regarding whether or not these “normal” levels are really adequate. Research is still in progress. Can a supplement really make up the difference? And are these “normal” levels reflective of what are more likely the optimal levels? Some doctors think that the optimal levels – those levels that best maintain health, without toxicity – are even higher. Other doctors are wary that too much vitamin D as a supplement can lead to toxicity and other adverse effects.

And how much should you take? Well, this is where it gets tricky – depending on your family history, and your own measured levels, your diet, and your overall health, the answer may be very different for one person than another. There is at least one study suggesting that we absorb lesser amounts more effectively than larger amounts. I suggest that you get your blood tested, and talk to your doctor about it before you pick a product off the shelf on your own.

Here's a good article from WebMD

2NIH (National Institutes of Health) web page describing vitamin D

Yes, I check vitamin D levels: I believe that people with specific conditions need more, and I frequently recommend moderate doses for my patients. Most of us don’t have enough in our bloodstream, and it affects so many bodily processes, that it’s impossible to ignore its importance in overall health. Get tested first. – Victoria Rhoades, ND