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Alkaline Phosphatase Level A Tipoff To Osteoporosis

Osteoporosis has compromised the vitality of 15 million to 20 million people in the United States, slowly thinning and weakening the bones and causing stooped posture, chronic aching and, in serious cases, bone fractures.

This condition affects approximately half of women age 45 and older, developing as they move from perimenopause -- the period around the onset of menopause -- into full-blown menopause, which is one year after the last menstrual cycle.

But in a recent study, Jane Lukacs, M.S.N., Ph.D., a University of Michigan Health System research fellow, and a team of researchers, found that a substance commonly checked during a simple and inexpensive blood test may give women in the early stages of perimenopause the warning they need to prevent osteoporosis.

The study of 38 healthy, non-smoking women between the ages of 40 and 54 suggested that elevated concentrations of alkaline phosphatase -- even levels within the normal range of the enzyme -- may indicate an increased level of bone cell activity and, therefore, potential bone loss. The enzyme level is usually measured as part of a routine blood test.

The study results were recently published in the Journal of Women's Health & Gender-Based Medicine.

"We looked specifically at women who were having menopausal complaint and irregular cycles," Lukacs says. "What I found is that women who are slightly further along in the process have elevated levels of serum alkaline phosphatase. This common marker done in laboratory tests can be utilized to indicate increased bone activity, and generally when you have increased bone activity you're going to have bone loss in the near future."

Bone cell activity is a normal occurrence marked by the breaking down and rebuilding of bone at remodeling sites. When estrogen levels decrease after menopause, the remodeling rate increases, but the process of rebuilding the bone is not as efficient. That results in net loss of bone.

Alkaline phosphatase is attached to the outside of bone-forming cells called osteoblasts. Alkaline phosphatase levels rise with the increased bone activity.

But alkaline phosphatase also can be found in other organ systems, Lukacs says. In order to be sure that the increased enzyme levels were a result of the bone activity, the study participants had fasted, eliminating the elevations in alkaline phosphatase that could occur in the intestines after a fatty meal.

Lukacs checked other measures of liver function to ensure the alkaline phosphatase levels were not influenced by the liver. With those accounted for, the increase in production of alkaline phosphatase could be attributed to the increased bone activity, suggesting bone loss.

Normally, this enzyme level is between 30 and 130 international units per liter of blood.

"On the whole, our results showed that where we found elevations, they were still within the normal range," Lukacs says. "Women who have increased or elevated levels within this normal range were generally at about 80 international units per liter -- well within the normal range -- but certainly, in this sample, indicating an increase in bone turnover."

Not only is it easy and inexpensive to test for alkaline phosphatase, but the routine nature of the testing may allow for earlier detection of increased bone activity.

"It's important for women to know early that they could be facing the risk of bone loss, simply because there are behaviors that they can do to preserve bone," Lukacs says. "Certainly one would want to exercise, and eat a very balanced nutritious diet that incorporates calcium and vitamin D in the diet. But even though you've incorporated lifestyle changes, it's not going to prevent bone loss. But perhaps it will slow the rate."

Menopause is the time in a woman's life when the ovaries stop producing estrogen and she ceases menstruating. This generally occurs around the age of 50. The loss of estrogen is associated with an increased rate of bone turnover and loss of calcium from the bone, which means that postmenopausal women are at an increased risk for bone loss.

Those who are at higher risk for developing osteoporosis include women who have reached menopause, women who have had ovaries removed, people who have a family history of the disease, those with a slender body frame and those who smoke, drink alcohol or eat few calcium-rich dairy products. Men also can be prone to osteoporosis.

Lukacs recommends that women who are experiencing signs of menopause such as night sweats, hot flashes or irregular cycles should discuss bone loss and osteoporosis with their physicians. If a routine blood test is a part of that visit, women may want to go a step further.

"It might be interesting to ask the physician, 'How was my serum alkaline phosphatase?'" Lukacs says. "If there is blood work done, more than likely this test is incorporated in it."

If the serum alkaline levels indicate increased bone activity, the physician and patient may decide to perform a more definitive test to determine osteoporosis risk, such as the bone mineral density test.

"The benefit to knowing that you've got increased bone activity is that it's probably going to stimulate you to do something or consider alternatives that you may choose once you've reached menopause," she says. "And of course one of those decisions will be whether you want any type of pharmacological intervention, whether it's hormone replacement or treatment with another drug that may prevent bone loss."

In future studies, Lukacs hopes to confirm the clinical significance of this finding by including bone density measurements.

Facts about bone loss, osteoporosis and menopause:

Adequate calcium, vitamin D, appropriate exercise and, in some cases, medication are important for maintaining bone health.

Women are not alone in their risk for osteoporosis. Today, 2 million American men have osteoporosis and another 3 million are at risk for this disease.

Menopause is the time in a woman's life when she ceases to menstruate. Menopause happens to all women, but affects each woman uniquely. It is a natural process that results when the number of follicles in the ovaries decline and stop producing estrogen, ending the monthly release of an egg. Because estrogen helps to keep calcium in the bones, postmenopausal women are at increased risk for bone loss and osteoporosis.

Most women spend one-third to one-half of their lifetime in postmenopause.

Bone building occurs over a lifetime. But it's particularly important during adolescence because that's the last time there is major building of bones. Teenagers, especially girls, need to be certain they are getting enough calcium in their diets. A deficiency in adolescence could lay the groundwork for osteoporosis later in life. - By Valerie Gliem

Related websites:

U-M Health Topics A to Z: Osteoporosis

U-M Health Topics A to Z: Menopause

U-M Health Topics A to Z: Non-Exercise Dangers

National Osteoporosis Foundation

North American Menopause Society

[Contact: Valerie Gliem, Kara Gavin ]






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