RESEARCH - Link between vitamin A levels and risk of fractures questioned

[Guest guest]

Link between high vitamin A levels and increased risk of fractures

questioned by new study

Rheumawire

Sep 8, 2004

Zosia Chustecka

A new study questions the link between high vitamin A intake and

osteoporosis. Two recent studies [1, 2] have suggested that high levels

of vitamin A increase the risk of fractures, and have lead to concerns

that the routine use of vitamin supplements and fortification of foods

with vitamin A may be harmful in Western countries, where the prevalence

of osteoporosis in increasing.

The new study, reported in Osteoporosis International, looked at the use

of vitamin supplements as well as the intake of vitamin A in foodstuffs

in order to determine whether they were associated with an increased

risk of fractures [3].

" The results from our study largely fail to confirm this association, "

the US researchers conclude.

Researchers from the division of epidemiology at the University of

Minnesota examined data from the huge Iowa Women's Health Study, a

longitudinal investigation involving 41 836 postmenopausal women (aged

55-69 years). The mean follow up for incident self-reported fractures

was 9.5 years

The team found no evidence of an increased risk of all fractures among

postmenopausal women who took vitamin supplements (n=6502). They did

find a slightly increased (1.18-fold) risk of incident hip fractures

(n=525), but note that there was no evidence of a dose-response

relationship in hip fracture risk with increasing amounts of vitamin A

or retinol from supplements. Also, the results show no association

between vitamin A and retinol intake from food and supplements, or food

only, and the risk of all fractures or hip fractures.

One of the strengths of this study is its size, which allowed an

adequate number of relatively rare events to be captured, and good

statistical power, the researchers comment. However, the estimate of

vitamin A intake was based on only 1 food frequency questionnaire, so it

is open to " random error, which would tend to attenuate our relative

risk estimates towards the null, " they comment.

The 2 previous studies that had found an increase in the risk of

fractures with high vitamin A intake were based on more accurate

estimates of vitamin A intake. The Nurses Health Study[2] determined

intake from 5 food frequency questionnaires, and was also a larger study

(n=72 337) with longer follow-up (18 years), and a broader range of ages

(33-77 years). The other study was smaller and shorter, being based on

data from the Uppsala Longitudinal Study of Adult Men (n=2322, aged

range 49-50, follow up of 3 years)[3].. But this study was the first to

use a biological marker of vitamin A, serum retinol, and it found a

direct link between serum retinol levels and the risk of fracture, with

high levels substantially increasing the overall risk of fracture, as

reported earlier this year by rheumawire.

Sources

Feskanich D, Singh V, Willett WC, Colditz GA. Vitamin

A intake and hip fractures among postmenopausal women. JAMA 2002 Jan 2;

287(1):47-54.

sson K, Lithell H, Vessby B and Melhus H. Serum

retinol levels and the risk of fracture. N Engl J Med 2003;

348:287-294.

Lim LS, Harnack LJ, Lazovich D & Folsom AR. Vitamin A

intake and the risk of hip fracture in postmenopausal women: the Iowa

Women's Health Study. Osteopros Int 2004; 15:552-559.

I'll tell you where to go!

Mayo Clinic in Rochester

http://www.mayoclinic.org/rochester

s Hopkins Medicine

http://www.hopkinsmedicine.org