High vitamin A intake increases risk of hip fractures
A diet rich in retinol (vitamin A) increases the risk
of hip fractures in postmenopausal women, researchers have confirmed.
Dr Diane Feskanich, Brigham and Women's Hospital,
Boston, Massachusetts, and colleagues speculated that long-term consumption
of high levels of vitamin A might contribute to osteoporosis and hip fractures.
They looked at the relationship between vitamin A intake from foods and
supplements and risk of hip fracture in 72,337 postmenopausal women taking
part in the Nurses' Health Study in the United States.
The researchers found that for women consuming the
most vitamin A (3,000µg of retinol equivalents per day or more) compared
with those consuming the least (less than 1,250µg per day), the relative
risk of hip fracture was 1.48 (95 per cent confidence interval, 1.05–2.07,
P=0.003). They say that the increased risk was primarily attributable
to retinol and that beta-carotene did not contribute significantly to
fracture risk. The association between high retinol intake and fracture
risk was attenuated among women using postmenopausal oestrogens, they
say.
In an accompanying editorial (ibid, p102), Dr Margo
Denke, Centre for Human Nutrition, University of Texas, Dallas, said:
"The findings of Feskanich et al provide further support for [determining]
a safe upper limit for dietary retinol." She comments that the observation
that risk of hip fracture was higher among women not taking oestrogens
was intriguing. "Oestrogens are known to block several steps in osteoclast
function, including differentiation, activation, and programmed cell death,
supporting the possibility that oestrogen could oppose the type of effects
expected of retinoic acid [a metabolite of retinol]." She concludes: "This
study serves as a reminder that vitamins are potent, essential nutrients
which have effects that can precipitate harm as well as provide benefit."
Correction
This study was published in the JAMA (2002;287:47). |
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