How large was the FIT trial?

FIT-2 enrolled 4,432 postmenopausal women with low femoral neck BMD but no baseline vertebral fractures. Combined with FIT-1 (2,027 women with existing vertebral fractures), the total FIT program included over 6,400 participants.

What dose of alendronate was used in FIT?

Participants started on 5 mg daily. The dose was increased to 10 mg daily during the trial based on emerging dose-response data. The 10 mg dose became the standard approved dose for treatment.

Did FIT show hip fracture reduction?

In the overall FIT-2 cohort (women without prior vertebral fractures), the hip fracture reduction was not statistically significant. A subgroup with T-scores at or below −2.5 did show a significant reduction. FIT-1, which enrolled higher-risk women, did demonstrate significant hip fracture reduction.

How long did FIT participants take alendronate?

The mean follow-up was approximately 3.8 years. The trial design did not extend beyond about 4.5 years, leaving long-term duration and drug holiday questions for later studies like FLEX.

Were men included in FIT?

No. FIT enrolled only postmenopausal women. Evidence for alendronate use in men with osteoporosis comes from separate, smaller trials.

Is alendronate still first-line for osteoporosis?

Yes. Most major guidelines, including those from the Endocrine Society and the American College of Physicians, recommend oral bisphosphonates (alendronate or risedronate) as initial pharmacotherapy for most patients with osteoporosis, citing FIT and related data.

What are the main safety concerns with long-term alendronate use?

Atypical femoral fractures and osteonecrosis of the jaw are rare but recognized risks with prolonged bisphosphonate exposure. These were not identified during FIT but emerged from post-marketing surveillance and later studies. Current guidelines recommend reassessment after 3 to 5 years of oral therapy.

Did all FIT participants take calcium and vitamin D?

Yes. All participants received supplemental calcium (500 mg/day) and vitamin D (250 IU/day). The fracture reduction seen in FIT reflects alendronate added to baseline supplementation, not alendronate alone.

How does FIT compare to trials of newer osteoporosis drugs?

FIT compared alendronate to placebo. Head-to-head comparisons with denosumab, zoledronic acid, and romosozumab come from separate trials. These newer agents have shown advantages in specific populations (severe osteoporosis, injection preference, anabolic-first strategies), but alendronate remains the cost-effective default for many patients.

Should FIT change how I talk to patients about osteoporosis treatment?

FIT provides the clearest evidence that treating low BMD with a bisphosphonate prevents fractures, even in women who have not yet fractured. That makes it a useful reference in shared decision-making. The 47% relative risk reduction is meaningful, but the absolute benefit (NNT ~34 over 4 years) should also be communicated for informed consent.

What FIT (Fracture Intervention Trial) Actually Changes in Clinical Practice

By HealthRX Medical Team

Published May 25, 2026Updated May 25, 2026Last reviewed May 25, 2026

At a glance

| Detail | Value | |---|---| | Trial name | Fracture Intervention Trial (FIT) | | N | 4,432 | | Intervention | Alendronate 5 mg/day (increased to 10 mg/day during the trial) | | Comparator | Placebo | | Duration | Approximately 4 years (mean follow-up ~3.8 years) | | Primary endpoint | New morphometric vertebral fractures | | Key result | 47% relative risk reduction in vertebral fractures (RR 0.53 to 95% CI 0.41, 0.68) | | Published | 1998, JAMA |

Why FIT Still Matters

Before FIT, clinicians had calcium, vitamin D, and calcitonin. None had fracture-endpoint data strong enough to change practice at scale. FIT was the first large, placebo-controlled trial to demonstrate that an oral bisphosphonate could meaningfully reduce fractures in postmenopausal women with existing low bone mineral density (BMD). That single result turned alendronate into the most widely prescribed osteoporosis drug in the world and reshaped how regulatory agencies, insurers, and guideline panels approached bone health.

The trial was actually conducted in two arms. FIT-1 enrolled women who already had at least one vertebral fracture at baseline (the "vertebral fracture" arm, n = 2,027). FIT-2 enrolled women with low femoral neck BMD but no baseline vertebral fracture (the "clinical fracture" arm, n = 4,432). The results discussed here focus on the FIT-2 cohort, though the combined dataset has been analyzed extensively in subsequent publications.

Methodology: What Most Summaries Skip

Enrollment Criteria Were Specific

Participants were postmenopausal women aged 55 to 80 with femoral neck BMD T-scores of −1.6 or lower but without existing vertebral fractures. Women taking estrogen, bisphosphonates, or fluoride were excluded. So were those with serious comorbidities. This created a relatively healthy cohort that does not reflect the complexity of patients clinicians treat today, particularly those on polypharmacy or with renal impairment.

Dose Escalation Mid-Trial

Alendronate dosing started at 5 mg daily. Partway through, the protocol was amended to increase the dose to 10 mg daily based on emerging dose-response data. This is rarely mentioned in guideline summaries but has practical implications: the fracture reduction signal reflects a mixed exposure. Patients who remained on 5 mg for longer periods may have experienced somewhat less BMD gain than the headline numbers suggest.

Vertebral Fracture Assessment Was Morphometric

New vertebral fractures were identified by serial spine radiographs using a semi-quantitative grading method. This means many of the fractures counted were asymptomatic, detected only on imaging. The clinical relevance of preventing subclinical morphometric fractures is real (they predict future symptomatic fractures), but it is worth noting that the 47% reduction figure includes fractures patients never felt.

Calcium and Vitamin D Were Universal

All participants received calcium (500 mg/day) and vitamin D (250 IU/day). This is easy to overlook but critical. FIT did not test alendronate alone; it tested alendronate added to baseline supplementation. Clinicians who prescribe alendronate without ensuring adequate calcium and vitamin D intake are departing from the conditions under which the drug proved effective.

Results Beyond the Headline

Vertebral Fractures

The primary endpoint showed a 47% relative risk reduction (RR 0.53 to 95% CI 0.41, 0.68) for new morphometric vertebral fractures over approximately 4 years. The absolute risk reduction was roughly 2.9%, translating to a number needed to treat (NNT) of about 34 over the trial duration.

Clinical Vertebral Fractures

When restricted to clinically symptomatic vertebral fractures, the reduction was 36%. Smaller, but still statistically significant. This distinction matters because asymptomatic fractures carry different weight in shared decision-making conversations.

Hip Fractures

In FIT-2 specifically, the hip fracture reduction did not reach statistical significance. This is the result that gets buried. Among the subgroup of women with femoral neck T-scores of −2.5 or lower, hip fracture reduction was significant, but the overall FIT-2 population did not see a clear hip fracture benefit. The FIT-1 vertebral fracture arm did show significant hip fracture reduction, but that was a higher-risk cohort with existing vertebral fractures.

BMD Changes

Lumbar spine BMD increased by approximately 6.2% and femoral neck BMD by 4.1% over the trial period in the alendronate group, compared with minimal change in placebo.

| Outcome | Alendronate | Placebo | Relative Risk Reduction | NNT (4 yr) | |---|---|---|---|---| | Morphometric vertebral fracture | 7.9% | 14.1% | 47% | ~34 | | Clinical vertebral fracture | 2.3% | 3.6% | 36% | ~77 | | Hip fracture (overall FIT-2) | 0.9% | 1.1% | Not statistically significant |, | | Any clinical fracture | 12.3% | 14.1% | 13% | ~56 |

What Changed in Guidelines Because of FIT

The AACE/ACE and NOF/Endocrine Society Positions

FIT, combined with FIT-1, became the evidentiary backbone for recommending bisphosphonates as first-line therapy in postmenopausal osteoporosis. The National Osteoporosis Foundation guidelines cite FIT-era data as the basis for treating patients with T-scores at or below −2.5, or those with T-scores between −1.0 and −2.5 and elevated FRAX-calculated fracture risk.

FDA Labeling

The FDA-approved label for alendronate specifically references FIT data for its fracture prevention indications. The label includes both postmenopausal osteoporosis treatment and prevention, with the fracture reduction claims rooted in FIT outcomes. It also lists the 10 mg daily dose as the standard, reflecting the mid-trial dose escalation.

Treatment Thresholds

Before FIT, there was no broad consensus on when to start pharmacotherapy for low BMD without prior fracture. FIT-2 demonstrated benefit in this exact population, giving guideline panels the evidence to recommend treatment based on BMD criteria alone, without requiring a prior fracture as a prerequisite.

Limitations the Authors Acknowledged

The original publication and subsequent analyses flagged several constraints.

Population homogeneity. The trial enrolled almost exclusively white postmenopausal women. Evidence for other demographic groups was extrapolated, not directly tested. The Endocrine Society's 2019 guideline update notes this gap but still recommends bisphosphonates across demographics based on pooled evidence.

Renal exclusion. Women with significant renal impairment were excluded. Alendronate is contraindicated in patients with creatinine clearance below 35 mL/min, partly because the safety data from FIT simply do not cover this group.

GI tolerability in trial vs. practice. FIT participants were carefully instructed on proper dosing (fasting, upright positioning, water volume). Real-world adherence to these instructions is inconsistent, and GI side effects are a leading cause of discontinuation. FIT's tolerability data may overestimate what clinicians see in practice.

Duration questions. FIT ran for about 4 years. The optimal duration of bisphosphonate therapy became a major clinical question in subsequent decades. The FLEX extension study later examined 10-year outcomes and found that discontinuation after 5 years was reasonable for many patients, but FIT itself could not answer this.

What FIT Does Not Tell You About Today's Patients

The Drug Holiday Question

FIT generated enthusiasm for long-term bisphosphonate use, but it preceded awareness of atypical femoral fractures and osteonecrosis of the jaw with prolonged exposure. Current American Society for Bone and Mineral Research recommendations suggest reassessment after 3 to 5 years of oral bisphosphonate therapy, with drug holidays for patients at moderate risk. FIT's design could not have anticipated this, and its data should not be used to argue for indefinite treatment.

Head-to-Head Positioning

FIT compared alendronate to placebo. It tells you nothing about whether alendronate is better or worse than risedronate, zoledronic acid, denosumab, or romosozumab. Subsequent trials have provided those comparisons, and treatment selection today depends on factors (injection preference, renal function, fracture severity, rebound risk) that FIT never addressed.

Patients on Concurrent Osteoporosis-Relevant Medications

Aromatase inhibitor users, glucocorticoid-dependent patients, and those on proton pump inhibitors were not represented. The ACR glucocorticoid-induced osteoporosis guideline recommends bisphosphonates in this population, but the evidence base comes from separate, smaller trials rather than from FIT.

The Prescribing Shifts FIT Actually Caused

Bisphosphonates became default first-line therapy. Before FIT, hormone replacement therapy was the primary pharmacologic option for postmenopausal bone loss. FIT gave clinicians a non-hormonal alternative with fracture-endpoint evidence.
BMD testing expanded. Once there was a proven intervention for low BMD, screening with DXA became clinically actionable. FIT created the treatment rationale that justified population-level screening programs.
Generic alendronate became the cost benchmark. After patent expiration, alendronate's position as the best-studied, cheapest bisphosphonate made it the default against which newer agents had to justify their added cost. This pricing effect persists today.
Weekly dosing emerged from FIT follow-up. The daily dosing regimen in FIT was cumbersome. Subsequent bioequivalence studies led to the 70 mg weekly formulation, which improved adherence without repeating the full fracture endpoint trial.

Frequently asked questions

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References

Cummings SR, Black DM, Thompson DE, et al. Effect of alendronate on risk of fracture in women with low bone density but without vertebral fractures: results from the Fracture Intervention Trial. JAMA. 1998;280(24):2077-2082. PubMed
Black DM, Schwartz AV, Ensrud KE, et al. Effects of continuing or stopping alendronate after 5 years of treatment: the Fracture Intervention Trial Long-term Extension (FLEX). JAMA. 2006;296(24):2927-2938. PubMed
Cosman F, de Beur SJ, LeBoff MS, et al. Clinician's guide to prevention and treatment of osteoporosis. Osteoporos Int. 2014;25(10):2359-2381. PubMed
Eastell R, Rosen CJ, Black DM, et al. Pharmacological management of osteoporosis in postmenopausal women: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2019;104(5):1595-1622. PubMed
Shane E, Burr D, Abrahamsen B, et al. Atypical subtrochanteric and diaphyseal femoral fractures: second report of a task force of the ASBMR. J Bone Miner Res. 2014;29(1):1-23. PubMed
FDA. Fosamax (alendronate sodium) prescribing information. FDA Label