What's the Deal With Vitamin D?
As a primary care doctor, I’m always cautious about “cure-all” tendencies. By this, I mean that it can be tempting to spill the success of a remedy into other realms. Any such buzz is catchy, and we may even bend scientific scrutiny with our desires to make a laudable case.
Take vitamin D, for instance. The past few years have seen report after report about all of the amazing health improvements made possible by supplementation. Recent analyses, however, are pulling back a bit on these claims and in some regards, have even shown some harm with supplementation. Let's examine the current understanding of vitamin D supplementation and venture toward where this momentum might be heading.
Vitamin D Primer
With any educational piece on vitamin D, it is essential to review the basics. The active form of vitamin D is called 25-hydroxy-vitamin D (25-OH-D). It comes from a few sources who’s end-product is the 25-OH-D through metabolism in the liver. The most common source is via conversion of cholesterol to vitamin D3, which then goes on to the liver transformation.
Foods are often fortified with vitamin D2, which can also be converted. Examples include orange juice and whole milk/milk products. Occasionally, vitamin D3 is found naturally in foods such as fish and eggs (no sunlight needed). These D2 and D3 vitamins, which are converted to 25-OH-D in the liver, go on to convert to calcitrol in the kidneys. This calcitrol is key in bone health and likely helps to maintain the immune system.
If all this sounds confusing, don’t worry. It’s complicated!
The vitamin D that we take in as a supplement is either D2 or D3 and comes in a variety of doses.
Vitamin D Claims
When I was in medical school, I learned that vitamin D deficiency caused a condition called Ricketts. Period. This was the extent of studying the effects of deficiency. Black and white photos of children exhibiting the characteristically bowed legs of Ricketts revealed the gravity of severe deficiency. Of course, no one I had worked with had seen a first-hand case of Ricketts.
Enter a new era. Vitamin D supplementation heralds benefits literally from cradle to grave. Studies reveal, and are reported on, liberally hailing and praising vitamin D. Supplementation in breastfed babies improves well-being, including the preventing the future development of chronic diseases, such as diabetes. Vitamin D supplementation improves symptoms of depression and may prevent certain cancers, namely breast cancer. In the elderly, vitamin D supplementation can stave of death and disability arising from falls.
Hold the Phone!
It seemed that the general attitude was that basically everyone should have been taking vitamin D supplements. They can’t hurt, right? Wonderful claims were being made, and new outcomes were emerging from every corner. Recently, however, some drawbacks have been noted. For instance, large doses of vitamin D in some populations have not only failed to show benefits but have actually caused painful kidney stones.
Scientific analysis of claims such as those mentioned above confirms that the results are, for the most part, mixed and that no definitive conclusions can be drawn. As it stands, only two definitive recommendations have been made regarding vitamin D by the U.S. Preventative Task Force. The first is for institutionalized elderly women. In this case, supplementation of 800 IU per day, along with exercise, is recommended. The second recommends no more than 400 IU for post-menopausal women for preventing fractures (broken bones). Higher doses did not reveal any convincing improvements.
Screening for Low Levels
It is still recommended that individuals at risk for low vitamin D be screened by checking 25-OH-D levels. Higher-risk individuals include those with low sun exposure, who live in northern climates, and have dark-pigmented skin. Individuals found to be deficient should be treated accordingly under the guidance of a healthcare professional until levels are normalized.
Recent revelations in the benefits (or lack thereof) in vitamin D supplementation are a hard pill to swallow for those excited about all the reported benefits. Though failing to provide anything definitive at this point, further consensus is coming - likely in the next year, as experts weigh in and data is collected more widely. Remember, the goal is to help without causing harm. For the time being, consider avoiding higher doses of vitamin D and getting screened for low levels if you are in a high risk group.