If Taking Vitamin D Supplement, Check your Parathyroid Hormone Level

If Taking Vitamin D Supplement, Check your Parathyroid Hormone Level

Osteoporosis is much more common in women than in men. This is because women have less bone mass than men, tend to live longer and take in less calcium, and need the female hormone estrogen to keep their bones strong. If men live long enough, they are also at risk of getting osteoporosis later in life.

Osteoporosis is a problem in which bones are less dense and more fragile and thus at greater risk for fracture, even with a small amount of trauma. This disease often affects bones in the hip, spine, and wrist.After menopause women produce much less of the hormone estrogen. Estrogen helps women's bones stay strong. For example, it helps deposit calcium in the bones. Low levels of estrogen cause a weakening of the bones.chronic diseases that affect the kidneys, lungs, stomach, or intestines or change hormone levels (examples of such diseases are diabetes, hyperthyroidism, and heart failure).

Although ordinarily associated with women, sex hormones play a role in osteoporosis in both genders, most likely by controlling the birth and duration of life of both osteoclasts (bone breakers) and osteoblasts (bone builders).The ovaries produce most of the estrogen in the body, but it can also be formed in other tissues, such as body fat, skin, and muscle. After menopause, some amounts of estrogen continue to be manufactured in the peripheral body fat. Even though the ovaries have stopped producing estrogens directly, they continue to be a source of the male hormone testosterone, which converts into estradiol.

Vitamin D aids in the absorption of calcium, helping to form and maintain strong bones. Recently, research also suggests vitamin D may provide protection from osteoporosis, hypertension, cancer, and several autoimmune diseases.This is stimulated by a decrease in serum calcium, phosphate (PO43−) and parathyroid hormone (PTH) levels. It regulates calcium levels by increasing the absorption of calcium and phosphate from the gastrointestinal tract, increasing calcium and phosphate reabsorption in the kidneys and inhibiting the release of PTH.Calcitriol is also commonly used as a medication in the treatment of hypocalcemia and osteoporosis.

Vitamin D is a group of fat-soluble prohormones, the two major forms of which are vitamin D2 (or ergocalciferol) and vitamin D3 (or cholecalciferol). The term vitamin D also refers to metabolites and other analogues of these substances. Vitamin D3 is produced in skin exposed to sunlight, specifically ultraviolet B radiation.Calcitonin (some brand names: Calcimar, Miacalcin) is a hormone that helps prevent further bone loss and reduces the pain that some people have with osteoporosis.

In calcium homeostasis, 1,25-(OH)2D works in conjunction with parathyroid hormone (PTH) to produce its beneficial effects on the plasma levels of ionized calcium and phosphate . The physiologic loop starts with the calcium receptor of the parathyroid gland . When the level of ionized calcium in plasma falls, PTH is secreted by the parathyroid gland and stimulates the tightly regulated renal enzyme 25-OH-D-1-a-hydroxylase to make more 1,25-(OH)2D from the large circulating pool of 25-OH-D.

The resulting increase in 1,25-(OH)2D (with the rise in PTH) causes an increase in calcium transport within the intestine, bone, and kidney. All these events raise plasma calcium levels back to normal, which in turn is sensed by the calcium receptor of the parathyroid gland.Similarly vitamin D deficiency will result in inadequate 25-OH-D and 1,25-(OH)2D synthesis, inadequate calcium homeostasis, and a constantly elevated PTH level (i.e. secondary hyperparathyroidism).

Hypothyroidism (low blood levels of parathyroid hormone) is rare, and is often due to surgical removal of the parathyroid glands. Low levels of calcium (hypocalcemia) and low levels of phosphorus may occur. Oral doses of dihydrotachysterol (DHT), calcitriol, or ergocalciferol at high doses can assist in increasing serum calcium concentrations in people with hypoparathyroidism or pseudohypoparathyroidism.

Because the patterns of reforming and resorbing bone often vary from patient to patient, experts believe several different factors account for this problem. Important chemicals (such as estrogen, parathyroid hormone, and vitamin D) and blood factors that affect cell growth are involved with this process. Changes in levels of any of these factors could play a role in the development of osteoporosis.

Vitamin D intake should be sufficient to maintain calcium absorption and prevent increased parathyroid secretion throughout the year. To determine the level of intake that achieved the latter in elderly women,researchers studied the interrelations among vitamin D intake, serum 25-hydroxyvitamin D (25(OH)D) levels, and parathyroid hormone concentrations in a cross-sectional study of 333 healthy, white, postmenopausal women with low median calcium (408 mg a day) and vitamin D (112 IU a day) intakes.

They conclude that the dietary intake of more than 220 IU of vitamin D a day by postmenopausal women in Massachusetts may be sufficient to maintain constant serum 25(OH)D and parathyroid hormone concentrations throughout the year. Such an intake prevents a seasonal increase in parathyroid hormone secretion, with its possible deleterious skeletal effects.Even with a serum vitamin D level of more than 10 ng per milliliter, increased bone turnover and elevated parathyroid hormone values can occur.

A trial over women had to have serum 25(OH)D levels greater than 20 ng per milliliter (in some cases, after vitamin D supplementation) and normal levels of parathyroid hormone and alkaline phosphatase. Women in the two parathyroid hormone groups and those who received alendronate alone were all provided with calcium and vitamin D supplements, as needed, on the basis of dietary intake, and with weekly alendronate. Therefore, we believe that in this randomized, controlled trial, the changes in bone mineral density and biochemical changes seen in the parathyroid hormone groups were clearly due to the administration of parathyroid hormone.

A new study suggests that elderly women about to begin taking drugs for preventing the brittle bone disease osteoporosis should have their parathyroid hormone level checked first.

Low levels of vitamin D can lead to excessive levels of parathyroid hormone, a condition known as secondary hyperparathyroidism.

Among a group of women taking alendronate (well known by the brand name Fosamax) to treat osteoporosis, those with hyperparathyroidism showed less increase in bone mineral density than those with normal parathyroid hormone levels, Italian researchers found.

The findings "suggest the need to measure parathyroid hormone in elderly patients at high risk of secondary hyperparathyroidism before starting therapy, so as to implement strategies aimed at normalizing it," Dr. Antonella Barone of Galliera Hospital in Genoa, Italy, and colleagues state.

As many as half of older people may have hyperparathyroidism due to vitamin D deficiency, Barone and her team point out in the Journal of the American Geriatrics Society. Hyperparathyroidism leads to excessive leaching of calcium from the bones.

To investigate whether this might affect response to osteoporosis treatment, the researchers compared 91 women who received weekly treatment with alendronate or alendronate plus a vitamin D supplement known as calcitriol.

Women taking calcitriol showed significantly greater increases in bone mineral density than those who weren't given the vitamin.

Among the women who didn't take calcitriol, there was no change in average parathyroid hormone levels, but those who did take the vitamin showed significant reductions in levels of the hormone. Furthermore, the women whose parathyroid hormone level became normal -- regardless of whether or not they were on vitamin D -- showed greater increases in bone mineral density than those who continued to have hyperparathyroidism.

The study is the first to show a relationship between persistent hyperparathyroidism and worse response to alendronate, so it must be confirmed by other researchers, Barone and her team write.

It will also be important to find out if the effect is seen with other osteoporosis drugs, and to determine which form of vitamin D is most effective, and safest, for bringing parathyroid hormone levels back to normal, they conclude.


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