Researchers at UCLA tried to show that low vitamin D would make an autoimmune thyroid problem worse. Their experiment was based on the idea that vitamin D has a dampening effect on an excessive and inappropriate immune response in many areas of your body, so they figured this was likely to apply to the thyroid as well. This turned out not to be the case, but what they did find was rather surprising.

First they created two groups of mice, one with vitamin D in their diet and the other with none. Even before they started their experiment they found that the vitamin D deficient mice had low levels of thyroxine (t4), meaning they were actually hypothyroid prone when the experiment was conducted. When the experiment was performed, vitamin D lacking mice did not have an excessive immune response as expected. Rather, they developed persistent hyperthyroidism because their thyroid glands were less able to withstand the stress of the experiment and were more sensitive to the autoimmune antibodies that both sets of mice were being exposed to. Simply put, a lack of vitamin D makes your thyroid more susceptible to injury that could result in hyperthyroidism.

While this is an animal study, the findings are important. First, it means that a lack of vitamin D contributes to the possibility of low thyroid. Second, it means that many irritants are likely to aggravate your thyroid to a greater extent if you lack vitamin D. For example, there are many chemical irritants in the environment that irritate your thyroid gland, such as perchlorate and flouride. If you lack vitamin D you are more likely to be adversely affected by them.

This may be part of the reason that so many people feel metabolically worse and gain weight as the winter months move along. It is simple to make sure you take some extra D in the winter and doing so may help you keep your metabolism and thyroid from suffering the winter blues.