Vitamin D is probably one of the more popular supplements around – in large part because dosing suggestions have changed radically in the last several years.  A decade ago, a typical dose was at a very conservative 400 I.U a day, and much fear surrounded the apparent ease of overdosing this fat-soluble vitamin.  More acceptable dosing today ranges from 2,000 I.U. daily to sometimes 50,000 I.U once a week to achieve sufficiency. (A blood test should be done prior to starting any vitamin D regimen, however.)

Now that the importance of vitamin D has been much more solidified, many people are taking some type of vitamin D supplement. However, they aren’t all the same – in fact there are two main forms of it, and you should only be taking one of them in particular.

There are two types of vitamin D available, vitamin D2 and D3. Vitamin D2, known as ergocalciferol, is synthetic and is actually never produced in the body. It’s made by radiating a derivative (ergosterol) from the mold ergot. Most prescription forms of vitamin D are actually vitamin D2.

Vitamin D3, known as cholecalciferol, is the end product of several chemical transformations that occur in our bodies, starting in the skin, liver and eventually the kidney.

The majority of experts recommend that vitamin D3 is the only form that should be supplemented. Otherwise, vitamin D3 is found in some plant and animal foods, but not in large enough amounts.

Living even part time in winter climates, wearing sunscreen and clothing prevents vitamin D precursors from being made in the skin. Therefore, it’s important to supplement.

When you do supplement, it’s important to read the label. It should clearly say which form of vitamin D it contains, whether vitamin D2 or D3. The label may instead list “ergocalciferol” (vitamin D2) or “cholecalciferol” (vitamin D3).

A recent study highlighted the importance of taking the right form of vitamin D in athletes. It’s well known that vitamin D levels plummet in the winter months, and past studies have indicated that athletic performance may be improved when vitamin D levels are sufficient in the winter. Raising vitamin D to sufficient levels can decrease muscle pain as well.

This newer study had strength athletes take 3,800 IU vitamin D2 (ergocalciferol) each day for six weeks, through a heavy weight training period. Study investigators were hoping to see improved performance by reducing inflammation and speeding recovery from exercise-induced muscle damage.(1)

However, what the investigators found was that circulating blood levels of vitamin D3 were actually decreased, and the athletes actually had increased muscle damage after intense strength training. They weren’t sure why exactly the athletes had much greater muscle damage, however they were confident in recommending that strength athletes steer clear from vitamin D, in the D2 form.

Vitamin D is important – it has many functions in the body such as helping absorb calcium, boosting and balancing immune function, lowering blood pressure and keeping muscles strong as we age, among others.

Therefore, supplementing with vitamin D during the winter months is something everyone should consider – getting a simple blood test will tell you what your levels are, and where to go from there with supplementation. I’ve tested hundreds of patients over the years, and nearly all of them have low levels of vitamin D – it’s very common.  When you do supplement, make sure it’s vitamin D3, or cholecalciferol so you get the most benefit.

1. David Nieman, Nicholas Gillitt, R. Shanely, Dustin Dew, Mary Meaney, Beibei Luo. Vitamin D2 Supplementation Amplifies Eccentric Exercise-Induced Muscle Damage in NASCAR Pit Crew Athletes. Nutrients, 2013; 6 (1): 63