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Vitamin D Deficiency and Thyroid Disease

Theodore C. Friedman, M.D., Ph.D.

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. It was thought that

one of 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, cholecalciferol (vitamin D

2

), found mainly in

plants and ergocalciferol (vitamin D

3

), 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 also from dietary intake.

Vitamin D is found naturally in fish (such as salmon and sardines) and fish oils, eggs and

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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 problems. 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

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 occurs.

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 low

vitamin D levels will have relatively high PTH levels along 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

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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.

Dr. Friedman usually recommends measuring PTH, calcium, and 25-OH vitamin D to

determine if a patient does have vitamin D deficiency. 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. Additionally, the assay may not be that good at measuring the low levels of

vitamin D. In general, Dr. Friedman would recommend treatment of patients that have a 25-

OH vitamin D of less than 30 ng/dL, but these patients should have a PTH in the high

normal range. Optimal levels of 25-OH Vitamin D for patients with thyroid diseases are

probably 35-60 ng/dL It is unclear what to do with a patient with a PTH in the high normal

range and a completely normal 25-OH vitamin D level or the other way around for patients

with a low 25-OH vitamin D level but a completely normal PTH level.

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

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exposure, and 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. Because of our busy

schedule, many of us do not go outside during the day much and our sunlight exposure is

minimal. 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. An alternative is to go to a tanning salon for

approximately three times. Another alternative for replacing mild vitamin D deficiency is to

take two multivitamins a day. Each multivitamin contains 400 international units of vitamin

D so a total of 800 international units of vitamin D will correct mild cases of low vitamin D

levels. For more severe levels, the patient can take 50,000 international units of vitamin D

orally once or twice a week. This needs to be given by a prescription. If this treatment

regimen is used, the patient needs to be monitored carefully with calcium and 25-OH

vitamin D levels to make sure the patient is not over replaced with vitamin D. The patient

may need this level of treatment for approximately three months and should be checked

monthly. The main side effect of vitamin D therapy is overtreatment leading to

hypercalcemia.

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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.

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 also reducing blood sugar levels in patients with diabetes. Proper

vitamin D levels are needed to 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

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