The Latest Research on Auto-Immune Disease and Vitamin D

A new NIH-funded study reports that long-term use of vitamin D supplements reduced the incidence of auto-immune diseases such as rheumatoid arthritis, psoriasis, and Hashimoto's thyroiditis in a large population of Americans 50 and older. The subjects in this study were taking 2000IU of Vitamin D3 a day, and those who took them for two years or longer saw the greatest reduction in risk.

Vitamin D is perhaps best known for its role in building strong bones, and the market for vitamin D supplements has grown to over a billion dollars a year. However, recent research has cast doubts on the value of vitamin D supplements in preventing bone loss and osteoporosis. So this latest finding on vitamin D and auto-immune disease is welcome news for people who sell vitamin D supplements.

But it's also a textbook illustration of how scientific research (and nutrition research, in particular) works to either prove or disprove a hypothesis. It's usually a multi-step process. And in today's information economy, each incremental step in that process gets the same degree of fanfare and publicity. But this is not always warranted. Recognizing where we are in that process can help you put headlines in context and keep the information in perspective. So let's break it down, using this latest finding as an example.

How nutrition research works

Step 1: Observe a correlation

As is so often the case, the case for vitamin D as a possible preventive for auto-immune disease started with an almost random observation. Somebody noticed that multiple sclerosis is much more common in areas of the globe that lie north of 40 degrees latitude. In fact, the further from the equator you live, the higher your risk. 

Step 2: Propose a hypothesis

There are a number of possible explanations for this phenomenon. It could be something about the diet in more northern countries or other aspects of their lifestyle. It could have to do with a pathogen that is more common in colder temperatures. Another hypothesis was that vitamin D might be protective against multiple sclerosis. 

Sunlight hitting our exposed skin is one of the primary ways we get vitamin D. When you live further from the equator, there's less sunlight in winter, and colder temperatures mean you're less likely to be outside with your skin exposed. As a result, people who live further from the equator are more likely to be deficient in vitamin D. And maybe that has something to do with why they are more likely to have multiple sclerosis.

Once you have formulated a hypothesis ("Vitamin D helps...

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