Enough Vitamin D in the winter?

January 25, 2013 2 min read

Enough Vitamin D in the winter?

It is critical for you and your family to get Vitamin D (which is a hormone, by the way) in the right amount. I used to think that I was not deficient – after all, I live in California and I am outside biking, walking and gardening – without sunblock most of the time. But because of my vitamin D deficiency, I was losing bone mass.

Vitamin D increases calcium and phosphorus absorption by a whopping 50%.

At the time I did not understand the sun's ultraviolet rays and when these rays were strong enough to manufacture this vital nutrient. I thought that if the sun was shining and my skin was exposed, that would produce vitamin D.

Not all sunlight produces vitamin D. In fact, most of North America is now in Vitamin D Winter. Only one ultraviolet ray (UVB) produces vitamin D when it interacts with a pre-cholesterol just under the top layer of skin. The UVB ray is strongest when the sun is directly overhead. When the sun is at a 45-degree angle or less, the skin will not produce vitamin D. The closer one lives to the equator the more potential there is to produce vitamin D.

 Where I live, in the San Francisco Bay Area, vitamin D will not be produced through sun exposure from November through the end of March.

So how much vitamin D do you need?

It is hard to know exactly without testing and testing is not exact, but it will certainly put you in the ballpark. The test to take is 25, hydroxyvitamin D. Make sure that the correct test is ordered; don't take the 1,25 dihydroxyvitamin D. A good target is between 40-55 ng/ml. Labcorp is providing the most accurate testing presently.

What kind of vitamin D should you supplement with?

Vitamin D3, not Vitamin D2. Most people need at least 2,000 IU each day and some people need much more depending on digestive problems or other health issues that might impact vitamin D absorption. It is always best to work with a health care practitioner familiar with vitamin D.

If you are low what should you do?

1,000 IU of vitamin D3 should increase your blood level of 25 hydroxyvitamin D by 10 points. It takes up to 6 weeks to saturate your tissue levels. Test again in 6-8 weeks to see if you have reached your target.

TIP: When your shadow is taller than you are, you will not produce vitamin D.