Calcium

Why it happens in Crohn’s disease

Calcium balance in Crohn’s fails at several points simultaneously. Absorption is vitamin D-dependent, so the vitamin D deficiency endemic to this population directly reduces calcium uptake. Fat malabsorption makes it worse in a specific way: unabsorbed fatty acids bind calcium in the lumen to form insoluble soaps, which removes calcium from circulation and simultaneously frees oxalate to be absorbed — the reason calcium oxalate kidney stones are common after ileal resection. Many patients also avoid dairy, whether because of true lactose intolerance (more common with small bowel disease) or symptom-driven elimination. On top of all this, corticosteroids reduce intestinal calcium absorption, increase urinary calcium loss, and suppress osteoblast activity, while inflammatory cytokines such as TNF-α and IL-6 directly stimulate osteoclasts.

Who is most at risk

• Cumulative corticosteroid exposure — the single strongest modifiable risk factor
• Dairy avoidance or lactose intolerance
• Low body weight, malnutrition and amenorrhoea
• Extensive small bowel disease or resection with fat malabsorption
• Persistent active inflammation, which drives bone loss independently of steroids
• Smoking, which independently worsens both Crohn’s disease and bone density

Symptoms of deficiency

• Silent until fracture — bone loss produces no symptoms of its own
• Fragility fractures, particularly vertebral, which are often missed
• Height loss and kyphosis from vertebral compression
• Muscle cramps, tetany and perioral tingling in acute hypocalcaemia
• Chvostek and Trousseau signs when calcium falls sharply

Many of these overlap with Crohn’s disease itself, which is exactly why deficiencies are missed. Fatigue attributed to active disease is frequently anaemia, and neuropathy attributed to medication is sometimes B12.

How it is tested

Serum calcium is a poor indicator of bone health because it is tightly defended by parathyroid hormone at the expense of the skeleton — total body calcium can be badly depleted with a normal serum level. Correct measured calcium for albumin, which is frequently low in active Crohn’s. DXA scanning is the meaningful test and is recommended for patients with prolonged corticosteroid use, prior fragility fracture, low BMI, postmenopausal status or hypogonadism. Check vitamin D and parathyroid hormone alongside.

Replenishment protocols

Guidelines generally target 1,000–1,500 mg/day of total elemental calcium from diet plus supplements, paired with adequate vitamin D — calcium supplementation without vitamin D repletion is largely wasted, since absorption is the bottleneck. Calcium citrate is better absorbed than carbonate when gastric acid is reduced by proton pump inhibitors and does not require food. Split doses to 500 mg or less at a time, as absorption efficiency falls above that. Anyone starting a steroid course expected to last three months or more should have bone protection considered from the outset, not retrospectively. For patients with a history of calcium oxalate stones after ileal resection, calcium taken *with* meals is preferable: it binds oxalate in the gut lumen and reduces stone risk rather than increasing it.

Amounts reflect what gastroenterology literature and guidelines describe. The right dose for you depends on your test results, absorption and surgical history, so test first and work with your care team to personalise it.

Medication interactions

Prednisone and other corticosteroids are the dominant interaction and act through three separate mechanisms at once. Proton pump inhibitors reduce absorption of calcium carbonate specifically. Calcium binds levothyroxine, bisphosphonates, quinolone and tetracycline antibiotics, and oral iron — separate these by at least two hours. Cholestyramine reduces vitamin D absorption and therefore calcium uptake indirectly.

Sources

1. 1

   Prevalence and pathogenesis of osteoporosis in patients with inflammatory bowel disease

   Bernstein CN, Leslie WD. · Gastroenterology Clinics of North America · 2005 · PMID 15785432

2. 2

   Nutrients in the prevention of osteoporosis in patients with inflammatory bowel diseases

   Ratajczak AE, Rychter AM, Zawada A, Dobrowolska A, Krela-Kaźmierczak I. · Nutrients · 2020

3. 3

   Osteoporosis in inflammatory bowel disease

   Ali T, Lam D, Bronze MS, Humphrey MB. · American Journal of Medicine · 2009