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Better Nutrition (1989-90)

Vitamin A influences thyroid function

Vitamin A influences thyroid function

Stephen Langer

Vitamin A Influences Thyroid Function

Among vitamin A’s many functions are keeping eyes healthy, aiding in cancer prevention and keeping the thyroid gland healthy.

Sometimes we are surprised to learn there’s more to an old friend than we thought. It’s the same with our old friend vitamin A.

Most of us know that vitamin A is basic to making and keeping healthy bones, eyes, glands, hair, skin and teeth.

We also know that it keeps mucous membranes healthy, boosts resistance to respiratory infections and various cancers, shortens periods of illness and helps night vision.

One of the lesser known facts about vitamin A is that it contributes to the development of sperm cells in males and eggs in women. You and I wouldn’t have been born if it weren’t for vitamin A, as well as other key vitamins and minerals.

Vitamin A occurs in two forms: retinol and beta-carotene. Retinol comes from meat, animal products, poultry and fish. Beta-carotene comes from vegetables and fruit and was given its name because it was first isolated from carrots, one of the richest sources of this substance.

Beta-carotene, which may treat and prevent certain forms of cancer, is actually a vitamin A precursor, which is not always transformed into vitamin A. This phenomenon has been well demonstrated in a biochemistry classic, Vitamins in Endocrine Metabolism, by Isobel Jennings of University College, University of Cambridge, England.

Individuals with low thyroid function (hypothyroidism) have a reduced ability to change beta-carotene into true vitamin A.

Why is this important? Because far more of the population is hypothyroid than we realize, and most of them are unaware of it. When the late Broda O. Barnes, M.D., Ph.D., world-renowned thyroid authority, first told me that an estimated 40 percent of the population has low thyroid function, most of them undiagnosed, I doubted the figure.

Then I found in my medical practice that the Barnes estimate was actually a bit too low, that many patients with the most prominent symptoms of this disorder — deep fatigue and cold hands and feet, or a cold nature in general — had not been responsive to conventional lab tests. These tests are specific for the ailment but now sensitive enough to reveal all cases.

Other alternative practitioners with whom I have compared notes have made similar findings and several researchers have found that many hypothyroids are not properly diagnosed.

Vitamin A is of utmost importance to the thyroid gland and its proper function. Jennings cites studies in which animals who did not receive enough vitamin A were limited in their ability to produce thyroid-stimulating hormone (TSH). Without enough of this hormone, thyroid gland activity is sluggish and so are we.

Vitamin A-deficient cattle and sheep show degeneration of the area of the pituitary gland where the TSH is synthesized.

The pituitary is the quarterback of glands. It calls the signals for other glands and heavily influences the thyroid. It controls the structure and output of the thyroid gland by means of TSH, ensuring that there is enough thyroid hormone in blood circulating to our trillions of cells. Thyroid hormone acts as a carburetor to regulate cell metabolism.

Vitamin A intake also influences the thyroid gland in another way. Sufficient vitamin A — not beta-carotene in this instance — must be present for the thyroid gland to absorb enough iodine, upon which it depends for proper function.

Beyond its influence on the thyroid gland, vitamin A, in conjunction with protein, contributes a great deal to the health of our eyes. In a fascinating study done in India, the suffering of nearly 100,000 children from kwashiorkor, the protein deficiency disease, motivated an American medical relief team to fly in to help.

Kwashiorkor’s main symptoms are wasting tissues, sluggish body and mind, swollen bellies, eye ailments, occasionally blindness, and even mental retardation. The relief team fed the children high-grade protein in the form of powdered skim milk, expecting them to recover within weeks.

However, week after week, their condition continued to worsen. A second medical team flew in to assist, among them doctors who specialized in eye disorders. Noting that most of the patients had eye ailments, they added vitamin A to their daily diet.

The vitamin A plus the protein-rich diet brought about a dramatic switch. The eye ailments began to clear up, and with them the other symptoms of protein deficiency.

Then the doctors ran lengthy tests and evaluated the results. They concluded that vitamin A must accompany protein to make it available to the body.

Several other factors about good old vitamin A should be considered in light of new information. For example, is the Recommended Dietary Allowance (RDA) for vitamin A adequate? At 800 micrograms (mcg) for women and 1,000 mcg for men (4,000 and 5,000 I.U.s, respectively) some doctors say no.

Many doctors believe varying conditions make more of this vitamin necessary. We need more vitamin A as we gain weight. We require more in winter than in summer. Illness, particularly hepatitis, pneumonia and cancer, surgery or heavy drinking soon deplete our liver stores of vitamin A and call for putting more money in the liver bank.

Diabetics and those with an overactive thyroid require more than the average amount of vitamin A. Air-pollution and overly bright lighting deplete stores of vitamin A. I find this true particularly in male and female patients who use computers for many hours daily.

Then, too, are the destroyers of vitamin A: aspirin, barbiturates, benzoate and nitrates from preserved food and polluted water, and, among many others, an artificial lemon flavoring called citral.

I usually suggest to my patients a daily intake of a 10,000 International Unit capsule of vitamin A derived from fish liver oils. Consult your health practitioner to determine the amount of vitamin A appropriate for your needs.

PHOTO : Dairy products (especially cheese and butter) and carrots are excellent sources of vitamin

PHOTO : A.

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