Amino Acid Linked to Bone Fractures

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Amino Acid Linked to Bone Fractures

Monitoring homocysteine levels may offer protection against osteoporosis

By Gardner

WEDNESDAY, May 12 (HealthDayNews) -- High levels of homocysteine, an amino

acid found in the blood, appears to be a risk factor for hip fractures in

older

people.

Experts aren't yet sure, however, if homocysteine is the actual cause of the

fractures or if it is associated in a more " innocent " way.

If it were a cause, this finding could have a major public health impact

because homocysteine levels can be manipulated through dietary changes.

" Homocysteine can be easily lowered and that would potentially reduce the

risk, " said Dr. P. Kiel, senior author of one of two articles on the

subject appearing in the May 13 issue of the New England Journal of

Medicine. He

is also director of medical research at the Hebrew Rehabilitation Center in

Boston.

At present, however, " we aren't sure how important it is, " said Dr. Lawrence

G. Raisz, author of an accompanying editorial in the journal and a professor

of medicine at the University of Connecticut Health Center in Farmington.

Elevated homocysteine levels are already recognized as a risk factor for

cardiovascular disease as well as cognitive impairment. It's also known that

people with homocystinuria, a genetic disease marked by high levels of

homocysteine, have an increased prevalence of osteoporosis.

In the first study, Kiel and his colleagues decided to delve further into

the

subject by examining the association between homocysteine levels and the

risk

of hip fractures in a group of 825 men and 1,174 women ranging in age from

59

to 91.

The participants were divided into four groups, depending on their

homocysteine levels. Men in the highest quartile had almost four times the

risk of hip

fracture as men in the lowest quartile, while women in the top group had 1.9

times the risk.

The second study, this one done by researchers in the Netherlands, also

found

increased homocysteine levels seemed to be an independent risk factor for

osteoporotic fractures in a group of 2,406 men and women over the age of 55.

People in the highest quartile had about double the risk of fracture as

people in

the other three quartiles.

" The question still remains, is it the homocysteine itself or is the

homocysteine a marker for some other risk factor that has the direct adverse

effect on

the skeleton, " Kiel said.

The arguments in favor of homocysteine as a causal factor include the fact

that, in individuals with homocystinuria, high homocysteine levels weaken

the

collagen of the bones, Kiel noted.

" The Dutch study didn't see a difference in bone density to go with an

increase in fractures so the total amount of bone wasn't different, " Raisz

pointed

out. " It may be the quality of the bone. One possibility is that high

homocysteine levels cause bone of poorer quality to be made. "

It's also possible that other, associated phenomena may be responsible, such

as nutrition, low estrogen levels or some as yet unknown factor, Raisz

added.

For the moment, more studies are needed to try to get at the underlying

mechanisms at work.

If it does turn out that homocysteine levels are responsible for an

increased

risk of fractures, the solution could be as simple as increasing intake of

folic acid and vitamins B 6 and B 12, Kiel said.

SOURCES: P. Kiel, M.D., director, medical research, Hebrew

Rehabilitation Center, and associate professor, medicine, Harvard Medical

School, both

in Boston; Lawrence G. Raisz, M.D., professor, medicine, University of

Connecticut Health Center, and head, University of Connecticut Center for

Osteoporosis, both in Farmington; May 13, 2004, New England Journal of

Medicine

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