Though the epithet 'hard-headed' is not normally meant
to flatter, new research suggests that having plenty of
bone may actually be a good thing when it comes to mental
capacity. A study published in the January issue of
Archives of Neurology found low bone mineral density
(BMD) in the femoral neck bone doubled the risk of developing
Alzheimer's disease (AD) and all-cause dementia —
in women only. Could estrogen replacement therapy be the
answer?
DOUBLED
TROUBLE
The study was headed by Dr Zaldy Sy Tan of Boston's
Beth Israel Deaconess Medical Center. Dr Tan and his
colleagues followed the fate of 987 elderly people,
610 of whom were women, after they had a baseline BMD
measured between 1988 and 1989. The density measurements
were taken at the femoral neck, the bony trochanter
located on the upper part of the femur, and the radial
shaft.
Subjects were then followed for
eight years. During that time, 384 died and 95 developed
some form of dementia, of which 75 cases were considered
to be AD. The researchers then matched up the dementia
data with the baseline BMD information. When the range
of femoral neck BMDs was divided into four groups, 243
patients fell into the lowest group. Thirty-five, or
just over 14%, of these relatively mineral-deficient
folks developed dementia. Of these 35, 77% developed
AD. Of the 744 patients in the three remaining BMD quartiles,
only 60, or a mere 8.1%, developed dementia — 75%
of which represented AD.
So, while dementia was always more
than likely to be of the Alzheimer's variety, the odds
of dementia were about twice as high in those with a
mineral-light femoral neck bone.
This increased risk remained significant
when the data was adjusted to rule out the influences
of age, smoking, stroke, estrogen use, level of education,
an apolipoprotein E marker and baseline homocysteine
level. Interestingly, however, no relationship was apparent
between femoral neck BMD levels, or indeed any BMD levels,
and either AD or all-cause dementia in men.
Women, in addition to showing the
femoral neck BMD-dementia correlation, displayed a similar,
though statistically insignificant, pattern for the
trochanter BMD. No relationship was evident, however,
between BMD measured at the radial shaft and the risk
of AD and all-cause dementia in the women.
The female-male dichotomy suggests
that cumulative estrogen exposure may influence the
increased AD risk, according to the researchers. They
concluded that estrogen supplementation may be a prudent
therapy in women with low BMD. This high-risk group
"may benefit from estrogen replacement therapy despite
the increased risk of nonneurologic complications,"
Dr Tan and colleagues wrote.
This latest study is likely to
stir up the hormone replacement therapy (HRT) debate
once more. Ever since the HRT debacle, which linked
this therapy to heart disease, stroke and breast cancer,
the estrogen treatment has had plenty of detractors
who point to side effects and a suspected link to the
increased risk of endometrial cancer as reasons to forego
the therapy. Dr Tan and his colleagues await other studies
to confirm their results, which could point the way
to controlled trials in women with low BMD.
Arch Neurol 2005;62:107-11
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