How To Get All Of Your Nutrition From Food

Constructing A Meal Plan

Vitamin D

What good would our epic quest to create a nutritionally-complete meal plan be if we did not take a little detour right before the end? In this case we need to address the conundrum of vitamin D.

The thing is that vitamin D is not really a vitamin. It is more accurately described as a pro-hormone. In humans, it is produced by the interaction of ultraviolet rays with cholesterol in the skin. Vitamin D has long been known to impact bone health, and more recent evidence has been linking it with the immune, nervous, endocrine, cardiovascular, and digestive systems. So we'll just say that vitamin D is an important thing.

But we don't normally get it from food. Even the vitamin D we see here in the milk is there because the milk has been fortified. What we should be doing is getting regular sunshine. According to scientists, somewhere between 5 and 30 minutes between 10 AM and 3 PM at least twice a week to the face, arms, legs, or back without sunscreen usually lead to sufficient vitamin D synthesis.

Season, time of day, length of day, cloud cover, smog, skin melanin content, and sunscreen are among the factors that affect UV radiation exposure and vitamin D synthesis. Perhaps surprisingly, geographic latitude does not consistently predict average vitamin D levels in a population. However, certainly the average number of sunny days in a particular location is an important factor.

I was able to determine that my particular mid-northerly location enjoys the sun on approximately half of the days. So theoretically, I should be able to get enough vitamin D throughout the year to store up for those times when I may be going longer periods without exposure to the sun. If I only need to get this exposure an average of twice a week, this should be attainable in my location. That is, of course, assuming that I can gain access to the sun if it is out, and not be stuck indoors. In case you were wondering, the skin does not produce vitamin D when exposed to sunlight filtered through a window.

Now I used an online vitamin D tool developed by the Norwegian Institute to do some calculations. I wanted to know how much vitamin D I could expect my skin to produce when exposed to the sun at my location on a cloudless day with an average UV index. I learned that I should expect to produce 25 μg of vitamin D every four minutes.

That means every time I go outside to get the recommended 5 to 30 minutes of sun exposure, my body is producing somewhere between 30 and 190 μg (1200 – 7600 IU) of vitamin D. This obviously raises the question of why the IOM is recommending only 25 μg (600 IU) of vitamin D in their recommendations, but we must remember that this is the amount of dietary vitamin D suggested for those with a normal amount of sun exposure.

So we still have a vitamin D issue, and there doesn't seem to be too many ways around it. Drinking four cups of fortified milk a day would throw all of our calculations off, and we wouldn't want to do that. So we are forced to admit that the average person requires some level of additional supplementation of vitamin D, in order to meet the recommended levels.

According to a fair amount of research, the amount of vitamin D supplementation needed to sustain healthful levels of vitamin D in the blood range between 2,000 and 5,000 IU daily, with some studies showing benefits at dosages near 10,000 IU daily. Yet according to the 2010 updated IOM report on calcium and vitamin D, they declare that 600 IU is sufficient, and have set the upper level intake (UL) at 4,000 IU daily. To resolve this conundrum, it may be best to consult with a professional.

Of course, you could always just take a multivitamin every day in order to make sure you are getting a bare minimum of vitamin D. But I understand you might be hell-bent on avoiding multivitamins at all cost. So if you just can't get enough sunlight and want to supplement with vitamin D only, I wrote an article discussing the conflicting scientific research on vitamin D supplementation for you to peruse and enjoy.

For the rest of us, let's get back to making our final adjustments to our meal plan.