What happens when you take prednisone with calcium?
Prednisone is a synthetic glucocorticoid prescribed for autoimmune conditions, asthma, allergies, organ transplant immunosuppression, and many other inflammatory disorders. It is highly effective at suppressing inflammation but carries a long list of metabolic side effects, one of the most consequential being its effect on calcium balance and bone health.
Prednisone and other glucocorticoids interfere with calcium homeostasis through several mechanisms. They suppress intestinal absorption of dietary calcium by reducing calcium-binding protein expression and altering vitamin D-mediated calcium transport. At the same time, they increase urinary calcium excretion by reducing tubular reabsorption in the kidneys. The net effect is a negative calcium balance: less calcium enters the body, and more calcium leaves it, even when dietary intake is unchanged.
To compensate for the dropping serum calcium that would otherwise result, the parathyroid gland secretes more parathyroid hormone, which pulls calcium out of bone. The bone-resorbing osteoclasts get activated while the bone-building osteoblasts are simultaneously suppressed by direct glucocorticoid effects. The combined result is the most common cause of secondary osteoporosis: glucocorticoid-induced osteoporosis (GIO).
Why is this important?
Bone loss from glucocorticoids is fast and severe. The greatest decline in bone mineral density occurs within the first 3 to 6 months of therapy and can reach 10 to 15% in the first year. Fracture risk rises sharply with even modest doses; the relative risk of vertebral fracture roughly doubles at prednisone doses of 2.5 to 7.5 mg/day and continues to climb at higher doses. Because vertebral fractures are often silent, patients may not know they have occurred until height loss or chronic back pain become apparent.
This is why every major guideline, including the 2017 American College of Rheumatology guideline for glucocorticoid-induced osteoporosis, recommends calcium and vitamin D supplementation for essentially every adult who will be on prednisone (or equivalent) at 2.5 mg/day or more for 3 months or longer. Calcium alone is not enough to prevent bone loss, but it is a necessary foundation. Without adequate calcium intake, the negative calcium balance imposed by the drug becomes structural bone loss; with adequate calcium, much of the loss can be mitigated or, when combined with vitamin D and bisphosphonate therapy in higher-risk patients, prevented.
What should you do?
If you have been prescribed prednisone (or any glucocorticoid, including methylprednisolone, dexamethasone, or hydrocortisone) at a dose of 2.5 mg/day or higher for a course expected to last 3 months or longer, talk to your prescriber about a bone health plan.
The American College of Rheumatology recommends a total calcium intake of 1,000 to 1,200 mg/day, including diet plus supplements, along with 600 to 800 IU of vitamin D daily (with higher doses if you are deficient). For most adults in the United States, dietary calcium averages around 600 to 800 mg/day, so a supplement of 500 to 600 mg of elemental calcium will typically close the gap.
Split calcium supplements into two doses (for example, 500 mg with breakfast and 500 mg with dinner). The intestine absorbs calcium most efficiently in doses of 500 mg or less at a time. Take calcium with food, especially calcium carbonate, which requires stomach acid for solubility.
Higher-risk patients (postmenopausal women, men over 50, anyone with a fragility fracture history, anyone on prednisone 7.5 mg/day or higher for 3 months or longer) should also have a baseline bone density (DEXA) scan and discuss whether a bisphosphonate or other osteoporosis drug is appropriate.
Which specific products are affected?
All systemic glucocorticoids share this bone effect, though potency and duration affect the magnitude. Prednisone, prednisolone, methylprednisolone (Medrol), dexamethasone (Decadron), hydrocortisone (when used at supra-physiologic doses), and triamcinolone are all implicated. Inhaled corticosteroids at standard asthma doses have minimal bone effect, but high-dose inhaled steroids over years can also contribute.
Calcium supplements come in many forms: calcium carbonate (Caltrate, Os-Cal, Tums), calcium citrate (Citracal), calcium gluconate, and calcium lactate. Carbonate has the highest elemental calcium content per pill but needs food for absorption; citrate is better absorbed on an empty stomach and is the preferred form for people on acid-suppressing medications like proton pump inhibitors.
Vitamin D supplements (cholecalciferol/D3 or ergocalciferol/D2) should be combined with calcium for adults on glucocorticoids. The ACR recommends 600 to 800 IU/day for most adults, but those with measured deficiency may need 1,000 to 2,000 IU/day or higher under medical supervision.
Dietary sources of calcium count toward the total and should not be dismissed: dairy products, calcium-fortified plant milks and orange juice, leafy greens (kale, collards, broccoli), canned salmon and sardines with bones, and tofu set with calcium sulfate are all useful sources.
The bottom line
Prednisone causes rapid bone loss by impairing calcium absorption, increasing calcium excretion, and directly suppressing bone formation. Calcium and vitamin D supplementation is the foundation of bone protection for anyone on long-term glucocorticoid therapy. Aim for 1,000 to 1,200 mg of total daily calcium and 600 to 800 IU of vitamin D, and discuss bone density testing and additional therapy if you are on prednisone 2.5 mg/day or higher for 3 months or longer.