In a 70‑year‑old woman who has started Fosamax (alendronate) without calcium supplementation, is this a problem?

Yes, This Is a Problem—Calcium and Vitamin D Supplementation Are Essential When Taking Fosamax

Your 70-year-old patient must start calcium and vitamin D supplementation immediately because the FDA label for alendronate (Fosamax) explicitly warns that low blood calcium must be treated before starting the drug, and that alendronate may worsen pre-existing hypocalcemia. 1 The drug label further states that physicians may prescribe calcium and vitamin D to help prevent low calcium levels during alendronate treatment. 1

Why This Matters: The FDA Warning

• Alendronate can lower serum calcium levels, and if your patient has low blood calcium before starting treatment, it may worsen during therapy. 1
• Most people with low blood calcium have no symptoms, but some may develop muscle spasms, twitches, cramps, or numbness/tingling in fingers, toes, or around the mouth. 1
• The FDA label explicitly instructs physicians to prescribe calcium and vitamin D to help prevent hypocalcemia while patients take alendronate. 1

The Evidence Base: Calcium and Vitamin D Are Standard of Care

• All major osteoporosis guidelines recommend 1,200 mg calcium daily (total from diet + supplements) and 800 IU vitamin D daily for women over 70 years. 2
• Combined calcium and vitamin D supplementation reduces hip fracture risk by 16% (RR 0.84,95% CI 0.74–0.96) and overall fracture risk by 5% (RR 0.95% CI 0.90–0.99). 2
• High-dose vitamin D (≥800 IU/day) reduces hip fracture risk by 30% (HR 0.70,95% CI 0.58–0.86) and non-vertebral fracture risk by 14% (HR 0.86,95% CI 0.76–0.96) in adults 65 years and older. 2
• The NCCN Bone Health Task Force recommends optimizing calcium intake and vitamin D status before starting any bisphosphonate, and notes that vitamin D deficiency should be corrected before treating with intravenous bisphosphonates because hypocalcemia has been reported in patients with unrecognized vitamin D deficiency. 3

Practical Algorithm: How to Supplement This Patient

Step 1: Calculate Total Calcium Intake

• Estimate dietary calcium first. A typical non-dairy diet provides ~300 mg/day; each dairy serving (milk, yogurt, cheese) adds ~300 mg. 3
• If her dietary intake is 500–600 mg/day, add 600–700 mg elemental calcium via supplements to reach the 1,200 mg/day target. 3, 2
• Do not exceed 2,000 mg/day total calcium (diet + supplements) in adults over 50 years, as higher intakes increase kidney stone risk and may raise cardiovascular concerns. 3, 2

Step 2: Choose the Right Calcium Formulation

• Calcium carbonate (40% elemental calcium) is the most cost-effective option and should be taken with meals for optimal absorption. 3, 2
• Example regimen: calcium carbonate 500 mg twice daily with meals (provides ~400 mg elemental calcium per dose). 3, 2
• Divide calcium doses into ≤500–600 mg elemental calcium per administration for optimal intestinal absorption. 2
• If she takes a proton pump inhibitor, consider calcium citrate instead, as it does not require gastric acid for absorption. 2

Step 3: Add Vitamin D

• Prescribe 800 IU vitamin D daily (the dose recommended for women over 70 years). 2
• Target serum 25(OH)D level ≥30 ng/mL (75 nmol/L) for optimal bone health. 3, 2
• If she has documented vitamin D deficiency (<20 ng/mL), correct it first with ergocalciferol 50,000 IU weekly for 8 weeks, then recheck the level and start maintenance dosing. 3, 2
• Vitamin D3 (cholecalciferol) is preferred over vitamin D2 (ergocalciferol) for maintenance therapy, particularly for intermittent dosing regimens. 3, 2

Step 4: Timing Relative to Alendronate

• Alendronate must be taken on an empty stomach, first thing in the morning, with plain water only. 1
• Wait at least 30 minutes after taking alendronate before taking calcium, vitamin D, or any other supplements. 1
• Practical approach: Take alendronate upon waking, wait 30 minutes, eat breakfast, then take calcium carbonate with breakfast. 1

Does Calcium Supplementation Improve Alendronate Efficacy?

• In a 2-year randomized trial of 701 postmenopausal women with dietary calcium intake ≥800 mg/day plus 400 IU vitamin D, alendronate 10 mg/day with or without 1,000 mg supplemental calcium resulted in significantly greater increases in BMD (5.6–6.0% lumbar spine) than calcium alone (0.8%). 4
• Addition of supplemental calcium to alendronate had no significant effect on BMD (p = 0.29–0.97) but did result in a small, statistically significant additional reduction in urinary NTx (a bone turnover marker). 4
• The key finding: alendronate works well even without calcium supplementation if dietary calcium intake is adequate (≥800 mg/day), but calcium and vitamin D are still recommended to prevent hypocalcemia and optimize fracture prevention. 4

Important Safety Caveats

• Calcium supplementation modestly increases kidney stone risk (1 additional case per 273 women over 7 years), but dietary calcium does not. 3, 2
• Prioritize dietary calcium sources when possible (dairy products, fortified foods), as they carry lower risk than supplements. 3, 2
• Evidence on cardiovascular risk with calcium supplements is inconsistent and inconclusive, but some studies suggest a possible increased risk of myocardial infarction. 3
• Common side effects of calcium supplements include constipation and bloating. 3
• Monitor serum calcium and phosphorus at least every 3 months during chronic therapy. 2

Common Pitfalls to Avoid

• Do not prescribe calcium supplements without first calculating dietary intake—many patients already consume adequate calcium from diet and risk over-supplementation. 2
• Do not use low-dose vitamin D (≤400 IU/day)—such doses are ineffective for fracture prevention. 2
• Do not take calcium or any other supplements within 30 minutes of alendronate—this will impair alendronate absorption. 1
• Do not exceed 2,000 mg/day total calcium from all sources in adults over 50 years. 3, 2