Are Bisphosphonates Safe Long Term?

What Bisphosphonates Do and Why Duration Matters

Bisphosphonates bind tightly to hydroxyapatite crystals in bone and are absorbed by osteoclasts, the cells that break bone down. Once inside, they trigger osteoclast apoptosis, slowing bone resorption. Because they embed in the bone matrix, their pharmacological effect outlasts the dosing period by months to years.

The four drugs used clinically in the United States are alendronate (Fosamax, 70 mg weekly oral), risedronate (Actonel, 35 mg weekly or 150 mg monthly oral), ibandronate (Boniva, 150 mg monthly oral or 3 mg IV quarterly), and zoledronic acid (Reclast, 5 mg IV yearly). FDA prescribing information for zoledronic acid confirms all four carry the same class-level long-term risk language.

How Bone Remodeling Changes With Prolonged Use

Normal bone remodeling cycles every 3 to 4 months. Bisphosphonates suppress resorption enough that bone mineral density (BMD) rises for 3 to 5 years, then plateaus. After 5 years of oral therapy or 3 years of annual IV zoledronic acid, the fracture-reduction benefit for non-vertebral sites levels off for lower-risk patients, while high-risk patients (prior vertebral fracture, T-score below -2.5 while on therapy, or on glucocorticoids) continue to benefit from extended treatment.

A 2022 review in the Journal of Bone and Mineral Research confirmed that the residual anti-fracture effect of alendronate persists for at least 2 to 3 years after stopping, supporting the concept of a structured drug holiday rather than indefinite continuation.

The FLEX Trial: The Benchmark for Long-Term Data

The FLEX trial (N=1,099) randomized women who had taken alendronate for 5 years to either continue for 5 more years or switch to placebo. Women who continued showed a statistically significant reduction in clinical vertebral fractures (2.4% vs 5.3%; relative risk reduction 55%) but no statistically significant reduction in non-vertebral or hip fractures compared with the placebo group. FLEX trial, JAMA 2006. This is the primary evidence base for limiting routine continuation to 5 years in lower-risk patients.

Rare but Real Risks: Atypical Femoral Fractures and Osteonecrosis of the Jaw

Both risks exist. Both are rare. Keeping the absolute numbers in view matters for shared decision-making.

Atypical Femoral Fractures (AFF)

Atypical femoral fractures are low-energy, transverse fractures of the subtrochanteric femoral shaft. They are associated with prolonged bisphosphonate use and are thought to result from over-suppression of bone turnover, which may impair micro-crack repair.

The American Society for Bone and Mineral Research task force estimated AFF incidence at approximately 3.2 per 100,000 person-years at 2 years of bisphosphonate exposure, rising to 113.1 per 100,000 person-years beyond 8 years. ASBMR Task Force, JBMR 2014. To put this in context, hip fractures in untreated osteoporotic women occur at roughly 900 per 100,000 person-years, meaning the drug prevents far more fractures than it causes at the population level.

Patients on bisphosphonates who develop new thigh or groin pain should have bilateral femur X-rays. Presence of a cortical stress reaction requires stopping the drug and orthopedic evaluation. Teriparatide (Forteo) is sometimes used to accelerate healing after AFF.

Osteonecrosis of the Jaw (ONJ)

Osteonecrosis of the jaw involves exposed, necrotic bone in the jaw that fails to heal after 8 weeks despite appropriate care. Risk is dramatically higher with IV bisphosphonates used in oncology doses (monthly zoledronic acid 4 mg for bone metastases) than with the annual 5 mg dose used for osteoporosis.

For oral bisphosphonates at osteoporosis doses, the American Dental Association estimated ONJ risk at roughly 0.01 to 0.04% (1 to 4 per 10,000 patients). High-risk dental procedures (extractions, implants) should be completed before starting bisphosphonates when possible. Routine cleanings and fillings carry no meaningful additional ONJ risk.

How to Stop Prolia Safely: Denosumab Discontinuation

Denosumab (Prolia, 60 mg subcutaneous every 6 months) is not a bisphosphonate, but it is frequently used alongside or instead of bisphosphonates and deserves specific guidance here because stopping it incorrectly causes rapid, severe bone loss.

Why Stopping Prolia Is Dangerous Without a Bridge

Unlike bisphosphonates, denosumab does not incorporate into bone. It works by binding RANKL and preventing osteoclast activation. Once the drug clears (roughly 6 months after the last dose), RANKL activity rebounds sharply, causing a surge in bone resorption that can exceed pre-treatment levels.

A 2017 study in Osteoporosis International (N=23) found that patients who stopped denosumab without bridging therapy lost an average of 6.8% lumbar spine BMD within 12 months. More concerning, multiple vertebral fractures occurred in 7 of 23 patients (30%) within 1 year of stopping. Osteoporosis International 2017.

The Bridging Protocol

The Endocrine Society and the American Association of Clinical Endocrinologists both recommend transitioning patients off denosumab to an antiresorptive agent, typically a bisphosphonate. The general approach endorsed in clinical practice and consistent with guidelines published in JCEM is:

1. Give the final Prolia injection on schedule.
2. Wait 6 months (the normal dosing interval).
3. At that 6-month mark, begin alendronate 70 mg weekly or zoledronic acid 5 mg IV.
4. Measure bone turnover markers (serum CTX) at 3 and 6 months post-bisphosphonate to confirm resorption is controlled.

Some high-risk patients may need two annual infusions of zoledronic acid before full transition is confirmed. Never simply stop denosumab and observe.

DEXA T-Score vs Z-Score: What Each Number Actually Means

DEXA scans report two scores. Confusing them leads to missed diagnoses and unnecessary treatment.

T-Score

The T-score compares your BMD to the average peak bone mass of a healthy 30-year-old of the same sex. The World Health Organization diagnostic thresholds are:

• T-score at or above -1.0: normal
• T-score between -1.0 and -2.5: osteopenia
• T-score at or below -2.5: osteoporosis
• T-score at or below -2.5 with a fragility fracture: severe osteoporosis

T-scores drive treatment decisions in postmenopausal women and men over 50. WHO diagnostic criteria, NIH.

Z-Score

The Z-score compares your BMD to an age-matched, sex-matched reference population. A Z-score at or below -2.0 is defined as "below the expected range for age" and should trigger evaluation for secondary causes of bone loss (vitamin D deficiency, hyperparathyroidism, celiac disease, glucocorticoid excess, hypogonadism).

Z-scores are used as the primary diagnostic metric in premenopausal women, men under 50, and children. A 45-year-old woman with a T-score of -2.6 but a Z-score of -0.4 likely has age-appropriate bone loss, not primary osteoporosis. That distinction changes the workup entirely.

Should Everyone Take Calcium and Vitamin D?

Not everyone needs supplements. Diet-first is the correct approach, with supplementation filling gaps.

Calcium: Targets and Sources

Adults aged 19 to 50 need 1,000 mg of elemental calcium daily. Women over 50 and men over 70 need 1,200 mg daily. NIH Office of Dietary Supplements calcium fact sheet confirms these targets.

One cup of plain yogurt provides about 415 mg. One cup of fortified milk provides about 300 mg. Getting 700 to 900 mg from food and topping up with a 500 mg supplement is reasonable for most people who cannot hit targets through diet alone.

Calcium carbonate (the most common supplement) requires stomach acid for absorption and should be taken with food. Calcium citrate is absorbed without food and is preferred in patients on proton pump inhibitors.

A large meta-analysis in the BMJ (N=51,145) found that calcium supplements taken without food increased cardiovascular event risk by a modest but statistically significant 15 to 30%. BMJ 2011. Taking supplements with meals appears to reduce this signal, and dietary calcium does not carry the same risk.

Vitamin D: Who Needs What Dose

Vitamin D3 (cholecalciferol) is preferred over D2 because it raises serum 25-hydroxyvitamin D more efficiently. The recommended dietary allowance is 600 IU per day for adults under 70 and 800 IU for those over 70, but patients with documented deficiency (serum 25-OH-D below 20 ng/mL) typically need 1,500 to 2,000 IU daily to maintain sufficiency. Endocrine Society Clinical Practice Guideline 2011.

Patients on bisphosphonates must have adequate vitamin D. Both alendronate and zoledronic acid have reduced efficacy and increased hypocalcemia risk when given to vitamin D-deficient patients. Correcting deficiency before the first bisphosphonate dose is standard care.

Do Weighted Vests Help Bone Density?

Weighted vests are a low-cost, accessible intervention. The evidence is modest but real, particularly for hip bone density in postmenopausal women.

What the Research Shows

A randomized controlled trial by Snow and colleagues published in the American Journal of Clinical Nutrition followed 37 postmenopausal women who wore weighted vests (averaging 11% of body weight) during daily walking for 5 days per week over 12 months. The vest group had significantly less hip bone loss than controls. Hip BMD held stable in the vest group vs. A 1.0% decline in controls (P<0.05).

A separate 4-month trial in postmenopausal women found that weighted vest walking (5 to 10% body weight) combined with jumping significantly improved trochanteric BMD compared with controls. Cussler et al., JBMR 2003.

Practical Guidance on Weighted Vests

Start with 5% of body weight (approximately 7 to 10 lbs for most women) and walk for 30 minutes on most days. Increase vest weight by 2 to 4 lbs every 4 to 6 weeks as tolerated. Weighted vest walking does not replace pharmacotherapy for established osteoporosis but is a reasonable adjunct and may be sufficient as a standalone strategy for osteopenia.

Balance and fall prevention should be assessed before recommending weighted vests to patients with a prior fall history or significant balance impairment. The additional mass changes the wearer's center of gravity and may increase fall risk in unsteady patients.

Who Should Take Bisphosphonates: Current Guideline Thresholds

The National Osteoporosis Foundation (now Bone Health and Osteoporosis Foundation, BHOF) recommends initiating pharmacotherapy in postmenopausal women and men over 50 who meet any of the following criteria:

• Hip or vertebral fracture (clinical or morphometric)
• T-score at or below -2.5 at the femoral neck, total hip, or lumbar spine
• T-score between -1.0 and -2.5 plus 10-year hip fracture probability at or above 3% or major osteoporotic fracture probability at or above 20% by FRAX

BHOF Clinical Practice Guide 2022 specifies these thresholds. FRAX scores are calculated at WHO FRAX tool using clinical risk factors with or without femoral neck BMD.

Bisphosphonates are first-line for most patients who meet these criteria. Anabolic agents (teriparatide, abaloparatide, romosozumab) are reserved for very high-risk patients (T-score below -3.0, multiple vertebral fractures, or bisphosphonate failure) because of cost and administration complexity.

Managing a Drug Holiday: When and How to Stop Bisphosphonates Temporarily

A drug holiday means stopping bisphosphonate therapy for a defined period after adequate loading, monitoring BMD and bone turnover markers, and resuming if the patient's fracture risk climbs again.

Who Qualifies for a Holiday

The BHOF recommends considering a holiday in patients who:

• Completed 5 years of oral bisphosphonate or 3 years of IV zoledronic acid
• Have a T-score above -2.5 at the hip at the time of reassessment
• Have no history of clinical vertebral or hip fracture

High-risk patients (prior vertebral fracture, T-score below -2.5, or ongoing glucocorticoid use) should generally continue treatment or switch to an anabolic agent rather than taking a holiday.

What to Monitor During a Holiday

Measure serum CTX (C-terminal telopeptide of type 1 collagen) at 12 to 18 months off therapy. A CTX above 0.573 ng/mL (the upper limit of the premenopausal reference range) suggests bone resorption is accelerating and the patient should restart therapy. Repeat DEXA at 2 years. A T-score that has dropped below -2.5 or any new fracture warrants immediate treatment restart.

Dr. Robert Adler, writing in the Annals of Internal Medicine, noted: "The concept of a drug holiday reflects the fact that bisphosphonates persist in bone, but the duration of protection is not indefinite and varies between patients based on baseline risk."

Special Populations: Glucocorticoid-Induced Osteoporosis

Patients taking prednisone at 5 mg or more per day for 3 or more months face accelerated bone loss, with the sharpest decline in the first 6 to 12 months of therapy. The American College of Rheumatology (ACR) 2022 guidelines recommend:

• FRAX-based risk stratification at glucocorticoid initiation
• Starting a bisphosphonate in moderate- to high-risk patients (10-year major osteoporotic fracture probability above 10% in adults over 40)
• Calcium 1,000 to 1,200 mg per day and vitamin D 600 to 800 IU per day for all patients on chronic glucocorticoids

ACR 2022 Glucocorticoid-Induced Osteoporosis Guidelines classify patients into low, medium, and high risk using age, dose, and FRAX, with anabolic agents (teriparatide) preferred over bisphosphonates only in the very highest-risk group.

Premenopausal women on glucocorticoids present a particular challenge. The Z-score, not the T-score, guides treatment decisions here, and pharmacotherapy thresholds are more conservative given the risks of bisphosphonate use during reproductive years.