Vitamin D Deficiency and Thyroid Disease
Vitamin D Deficiency and Thyroid Diseases
Vitamin D is an important vitamin that not only regulates calcium, but also has many other beneficial actions. Not many endocrinologists realize this, but several articles published over 20 years ago showed that patients with hypothyroidism have low levels of vitamin D. This may lead to some of the bone problems related to hypothyroidism. Two mechanisms may explain the low levels of vitamin D in patients with hypothyroidism, 1) the low levels of vitamin D may be due to poor absorption of vitamin D from the intestine or 2) the body may not activate vitamin D properly. Other articles have demonstrated that patients with Graves disease also have low levels of Vitamin D. Importantly, both vitamin D and thyroid hormone bind to similar receptors called steroid hormone receptors. A different gene in the Vitamin D receptor was shown to predispose people to autoimmune thyroid disease including Graves’ disease and Hashimoto’s thyroiditis. For these reasons, it is important for patients with thyroid problems to understand how the vitamin D system works.
Sources of Vitamin D
Vitamin D is really two different compounds, ergocalciferol (vitamin D2), found mainly in plants and cholecalciferol (vitamin D3), found mainly in animals. Both of these hormones are collectively referred to as vitamin D, and they can either be obtained in two ways. One is by exposure of the skin to the ultraviolet (UV) rays of sunlight or from dietary intake. Vitamin D is found naturally in fish (such as salmon and sardines) and fish oils, eggs and cod liver oil. However, most Vitamin D is obtained from foods fortified with Vitamin D, especially milk and orange juice. Interestingly, as breast feeding has become more popular, the incidence of Vitamin D deficiency has increased as less fortified milk is consumed. Vitamin D deficiency may also occur in patients with malabsorption from their intestine, such as in the autoimmune disease called Celiac Disease, which occurs frequently in patients with thyroid conditions. Multivitamins also contain Vitamin D, as does some calcium supplements like Oscal-D and Citracal plus D.
Different Forms of Vitamin D and How To Diagnose Vitamin D Deficiency
Vitamin D itself is inactive and needs to get converted to the liver to 25-hydroxy vitamin D (25-OH vitamin D) and then in the kidney to 1,25-hydroxy vitamin D. It is only the 1,25- OH vitamin D which is biologically active. This form of vitamin D acts to allow for absorption of calcium from the intestinal tract. Therefore, patients with low vitamin D levels will have low calcium and in severe cases get rickets (in children) or osteomalacia (in adults) which is when the bone bows out and is poorly formed. In mild cases of vitamin D deficiency, osteoporosis can occur, but low calcium is rare.
The conversion from the 25-OH vitamin D to the 1, 25-OH vitamin D that occurs in the kidney is catalyzed by parathyroid hormone, also called PTH. Therefore, patients with very low vitamin D levels will have relatively high PTH levels often with low calcium levels. This is similar to patients with primary hypothyroidism having elevated TSH levels while having normal thyroid hormone levels. Additionally, the 25-OH vitamin D form which is the storage form and is much more abundant that the 1,25-OH vitamin D form which, although is active, is less abundant. Therefore, in states of vitamin D deficiency, low levels of 25-OH vitamin D are found, but the 1,25-OH vitamin D levels are either normal or actually slightly high. They are slightly high because the excess PTH that is stimulated by the low 25-OH vitamin D levels stimulates the conversion up to 25-OH vitamin D to the 1,25-OH vitamin D. Thus, patients that are vitamin D deficient usually have a low 25-OH vitamin D level, a high PTH level, a low normal calcium, and a normal or an elevated 1,25-OH vitamin D level. However, some patients may actually have a high normal calcium as the elevated PTH, and 1,25-OH vitamin D may cause increased calcium absorption from the GI track and reabsorption from the kidney. If 25-OH vitamin D levels were not measured, these patients might have been incorrectly diagnosed with mild hyperparathyroidism as they have a high normal calcium and a high PTH.
Dr. Friedman usually recommends measuring a 25-OH vitamin D to determine if a patient does have vitamin D deficiency. Occasionally, PTH and calcium, can also be ordered. The 25-OH vitamin D assay has a normal range of approximately 20-60 ng/dL. However, this range may be too low for many patients. In general, Dr. Friedman would recommend treatment of patients that have a 25-OH vitamin D of less than 30 ng/dL. Optimal levels of 25-OH Vitamin D for patients with thyroid diseases are probably 35-60 ng/dL.
Treatment of Vitamin D Deficiency
There are several ways to correct for the depletion of vitamin D, and these would involve either increasing sunlight exposure or increasing dietary intake. In general, Dr. Friedman feels there is an ongoing battle between endocrinologists and dermatologists about sunlight exposure, as mild sunlight exposure probably does not have that much of an increased risk of skin cancer yet would be helpful to prevent vitamin D deficiency. Dr. Friedman encourages his patient to be outside and get sunlight, but sunscreen can be use if needed. Because of our busy schedule, many of us do not go outside during the day much and our sunlight exposure is minimal. When we do go outside, we are usually covered up with clothes. Blacks and other dark-skinned patients absorb less Vitamin D and need more sunlight exposure. Dr. Friedman recommends a patient to be exposed to the sun for 15-30 minutes a day, especially in the morning, to correct for vitamin D deficiency. However, in northern latitudes, little light of the proper wavelength goes through the atmosphere in the winter, so this exposure needs to occur in the spring and summer at which time stores of vitamin D are built up. The body has mechanisms so that too much vitamin D can not be synthesized by prolonged sun exposure.
Replacing Vitamin D
When it comes to replacing Vitamin D, again we have to understand the difference between D2 (ergocalciferol, available by prescription) and D3 (cholecalciferol, available over-the-counter). Even though both forms of vitamin D are fat soluble, studies have shown that if you take D2, your levels rise, but then fall back to almost baseline in a few weeks. In contrast, after D3, the levels stay high for a longer period of time. Therefore Dr. Friedman only recommends D3 which can be purchased online at various doses. Multivitamins and preparations like Oscal D contain D3, however the amount in these preparations are small. For example, each multivitamin contains 400 international units of vitamin D3 so a total of 800 international units of vitamin D will probably not raise 25-OHD levels.
There are several options for vitamin D3 replacement. 5000 iU a day is a convenient option as its hard to get over or undertreated on that dose. For lower levels of 25-OHD the 50,000 iU dose can be taken once or twice a week, although occasionally patients need higher doses. Bio-tech has several excellent products including 50,000 iU o D3 is sold in bottles of 12 or 100 by bio-tech-pharm.com. Order at shop.biotechpharmacal.com. However, most brands are excellent.
Side Effect and Optimal Levels
The main side effect of vitamin D therapy is overtreatment leading to hypercalcemia. Because of this concern, Dr. Friedman usually recommends keeping the 25-OHD level less than 60 ng/dL. Patients with kidney problems cannot convert vitamin D to the active 1,25-OH vitamin D levels and need to take calcitriol which is 1,25-OH vitamin D. Additionally, patients with hypoparathyroidism are usually placed on the calcitriol as well.
Conclusion
Vitamin D appears to have many effects besides being related to calcium and bone health, although many studies were done with correlations and did not show clear beneficial effect of vitamin D replacement. Nevertheless, Dr. Friedman recommends keeping 25-OH vitamin D between 35 and 60 ng/dL. Some patients with low vitamin D levels have fatigue and bone pain, which is easily reversible with proper replacement of vitamin D. Vitamin D may protect against heart disease and some types of cancer. Vitamin D may also have some role in regulating the immune system and may have mild effects in reducing blood sugar levels in patients with diabetes, although Dr. Friedman published a study in Diabetes Care that this vitamin D had no effect in patients with prediabetes. Proper vitamin D levels can prevent osteoporosis. In conclusion, proper vitamin D levels are essential for one’s health, especially if you have thyroid problems. Unless a patient is exposed to sunlight or foods containing vitamin D, screening for Vitamin D deficiency is recommended for all thyroid patients.
This article is not intended to offer medical advice and is offered for information purposes only. Do not act or rely upon information from this article without seeking professional medical advice. For more information about Dr. Friedman or to schedule an appointment, please go to goodhormonehealth.com.