Vaginal Estradiol: Bone Health and Density Impact

What vaginal estradiol is approved for

The Estradiol Vaginal Cream, 0.01% label lists one indication: treatment of moderate to severe symptoms of vulvar and vaginal atrophy due to menopause [1]. The labeled regimen is 2 to 4 g daily for one or two weeks, then half that dose for a similar period, with a maintenance dose of 1 g one to three times a week once the vaginal lining has been restored [1]. Bone is not part of the indication.

The cream's boxed warning carries the longer format: endometrial cancer, cardiovascular disorders, breast cancer and probable dementia. It states that in the absence of comparable data, these risks should be assumed to be similar for other doses of conjugated estrogens and other dosage forms of estrogens [1].

Does vaginal estradiol change bone density?

The vaginal cream label does not include osteoporosis prevention as an indication [1]. The Cochrane review of intravaginal estrogens, first published in 2006 and updated in 2016, compared vaginal preparations for atrophy symptoms. Its primary outcomes were symptom improvement and endometrial thickness, not bone [6].

The label states that systemic absorption may occur and that the warnings, precautions and adverse reactions associated with oral estrogen treatment should be taken into account [1].

Where the bone evidence actually comes from

The oral estradiol tablet label carries a prevention of postmenopausal osteoporosis indication. It describes a two-year randomized, placebo-controlled, double-blind, dose-ranging study in which 0.5 mg of estradiol daily for 23 days of a 28-day cycle prevented vertebral bone mass loss in postmenopausal women [2]. The same label says that when estrogen therapy is stopped, bone mass declines at a rate comparable to the immediate postmenopausal period, and that there is no evidence estrogen replacement restores bone mass to premenopausal levels [2].

The Climara patch carries the same indication. Its label says to consider non-estrogen medications first when the only goal is preventing osteoporosis, and to consider the patch only for women at significant risk of osteoporosis [3].

The fracture numbers usually quoted come from the Women's Health Initiative, which used oral conjugated estrogens 0.625 mg, not estradiol and not a vaginal product. In the estrogen-alone substudy of 10,739 women with prior hysterectomy, the vaginal cream label's table lists a relative risk of 0.65 for hip fracture (95% CI 0.45 to 0.94), 0.64 for vertebral fracture (0.44 to 0.93) and 0.71 for total fractures (0.64 to 0.80) [5][1]. In the estrogen-plus-progestin substudy of 16,608 women with a uterus, the hip fracture hazard ratio was 0.66 (0.45 to 0.98) [7][2], and total hip bone mineral density rose 3.7% after three years versus 0.14% on placebo in a subset of 1,024 women [8].

The Climara boxed warning addresses how far those results travel: only daily oral conjugated estrogens 0.625 mg were studied, so the relevance of the WHI findings to lower doses, other routes of administration or other estrogen-alone products is not known [3].

Endogenous estradiol and fracture risk

Hormone-and-bone data in this area also come from the body's own estradiol. In the Study of Osteoporotic Fractures cohort of women 65 and older, women with undetectable serum estradiol (below 5 pg/mL) had a relative risk of 2.5 for later hip fracture (95% CI 1.4 to 4.6) and 2.5 for vertebral fracture (1.4 to 4.2) compared with women who had detectable estradiol; women taking estrogen were excluded [9]. This was an observational study of natural hormone levels, not of a vaginal product.

What guidance says about treating both problems

The 2022 North American Menopause Society position statement says hormone therapy remains the most effective treatment for vasomotor symptoms and genitourinary syndrome of menopause and has been shown to prevent bone loss and fracture [4]. For women younger than 60 or within 10 years of menopause onset without contraindications, it calls the benefit-risk ratio favorable for bothersome symptoms and for prevention of bone loss [4]. For bothersome genitourinary symptoms not relieved by over-the-counter products in women who have no indication for systemic hormone therapy, it recommends low-dose vaginal estrogen, vaginal dehydroepiandrosterone or oral ospemifene [4].

On screening, the US Preventive Services Task Force recommends bone measurement testing for women 65 and older and for younger postmenopausal women at increased risk of osteoporosis [10].

Another product with bone data

Bazedoxifene plus oral conjugated estrogens was tested in SMART-5, a phase 3 trial of 1,843 postmenopausal women with a uterus. At 12 months, lumbar spine and total hip bone mineral density rose significantly compared with decreases on placebo (P < 0.001) [12].

What the vaginal cream label says to watch for

The label lists contraindications including undiagnosed abnormal genital bleeding; known, suspected or past breast cancer; known or suspected estrogen-dependent neoplasia; active or prior deep vein thrombosis or pulmonary embolism; active or prior arterial thromboembolic disease such as stroke or myocardial infarction; known anaphylaxis or angioedema to the product; known liver dysfunction or disease; protein C, protein S or antithrombin deficiency or other thrombophilic disorders; and known or suspected pregnancy [1]. The label also says that if feasible, estrogens should be discontinued at least 4 to 6 weeks before surgery of a type associated with increased thromboembolism risk, or during prolonged immobilization [1].