Dr Bette Liu and colleagues from the United Kingdom determined whether transdermal compared with oral use of hormone replacement therapy reduces the risk of gallbladder disease in postmenopausal women.
The research team recruited 1,001,391 postmenopausal women between 1996 and 2001 from NHS breast screening centres.
The researchers followed the patients by record linkage.
The team also routinely collected NHS hospital admission data for gallbladder disease.
|The hospital admission rate per 100 women over 5 years for cholecystectomy was 2 with oral therapy|
|British Medical Journal|
The researchers used adjusted relative risk and standardized incidence rates of hospital admission for gallbladder disease or cholecystectomy according to use of hormone replacement therapy.
The team found that 19,889 women were admitted for gallbladder disease during follow-up.
The researchers noted that 86% of these women had a cholecystectomy.
Compared with never users of hormone replacement therapy, current users were more likely to be admitted for gallbladder disease.
However, the researchers observed that risks were substantially lower with transdermal therapy than with oral therapy.
The team found that among women using oral therapy, equine estrogens were associated with a slightly greater risk of gallbladder disease than estradiol.
The research team noted that higher doses of estrogen increased the risk more than lower doses.
The team found the risk of gallbladder disease decreased with time since stopping therapy.
Results were similar taking cholecystectomy as the outcome.
Standardized hospital admission rates per 100 women over 5 years for cholecystectomy were 1.1 in never users, 1.3 with transdermal therapy, and 2 with oral therapy.
Dr Liu's team concluded, "Gallbladder disease is common in postmenopausal women, and use of hormone replacement therapy increases the risk."
"Use of transdermal therapy rather than oral therapy over a 5 year period could avoid 1 cholecystectomy in every 140 users."