Vitamin D and Calcium in GI Disease

Dietary supplement (vitamin and mineral)

Vitamin D3 (cholecalciferol) and D2 (ergocalciferol) as tablets, drops, capsules or injections; calcium citrate and calcium carbonate; combined calcium plus vitamin D products. Brand names vary.

Vitamin D is made in the skin with sunlight and comes from some foods (oily fish, eggs, fortified products). It helps the gut absorb calcium and keeps bones and muscles healthy. Calcium is the main mineral in bone. When vitamin D or calcium is low, or when the gut absorbs poorly, the body takes calcium from bone, leading to thin bones (osteopenia and osteoporosis) and, in severe cases, soft bones (osteomalacia) and fractures. Gut and liver conditions raise this risk in several ways: coeliac disease and short bowel syndrome reduce absorption; inflammatory bowel disease causes inflammation, poor appetite and steroid use; cirrhosis and long-standing bile-duct diseases (PBC, PSC) impair vitamin D handling and fat absorption; chronic pancreatitis and bariatric surgery reduce fat-soluble vitamin absorption; and long-term use of acid-lowering medicines (proton pump inhibitors) has been linked in observational studies with a small rise in fracture risk, although the evidence is not strong and these medicines should not be stopped without medical advice. Professional guidance (for example from the AGA, ACG and ESPEN) recommends checking vitamin D and calcium, and considering a bone-density (DXA) scan, in people at high risk. In the general population, large trials of routine vitamin D and calcium (such as VITAL) did not show fewer fractures in people who were not deficient, so supplements are most useful when there is deficiency, malabsorption, steroid use or a high bone-loss risk.

Your doctor decides whether you need vitamin D, calcium or both, which form, and how often (daily, weekly or an occasional larger course). The right amount is individual: people with malabsorption often need more than the general advice, while people with high calcium or kidney stones may need less or none. Do not copy another person’s dose. Get most calcium from food first (dairy such as milk, laban, yoghurt and cheese, sardines with bones, tahini, almonds, fortified foods) and use supplements only to make up a shortfall. Calcium citrate is absorbed with or without food and does not rely on stomach acid, so it is usually preferred in people taking acid-reducing medicines or after bypass surgery; calcium carbonate is best taken with meals. Take calcium in smaller amounts spread through the day rather than all at once. Vitamin D is fat-soluble, so take it with a meal containing some fat; D3 is generally preferred. When the gut cannot absorb vitamin D, higher oral amounts, a different form, ultraviolet light or injections may be used under specialist advice. As a general safety guide, the Institute of Medicine’s tolerable upper intake levels for adults from all sources together are 4,000 IU (100 micrograms) a day for vitamin D, and 2,500 mg a day of calcium up to the age of 50 and 2,000 mg a day after 50; these are ceilings for the general population, not targets, and a specialist may sometimes treat above them with monitoring.

• Thirst, passing a lot of urine, nausea, vomiting, constipation, belly pain, weakness or confusion while taking vitamin D or calcium — Could be a high blood calcium level from too much vitamin D or calcium. Stop the supplement and seek urgent medical advice.

• Severe pain in the side or back, blood in the urine, or pain passing urine — Could be a kidney stone, which is more likely with too much calcium or vitamin D. See a doctor urgently.

• Fainting, chest pain or irregular heartbeat — Abnormal calcium levels can affect the heart. Go to the emergency department.

• New bone pain, muscle weakness, cramps or tingling, or a fracture after minor injury — May mean low vitamin D or calcium, soft bones or thin bones despite treatment. See your doctor promptly rather than waiting.

• Painful or difficult swallowing, chest pain behind the breastbone or heartburn after starting an oral osteoporosis tablet (bisphosphonate) — These tablets can irritate the food pipe. Stop them and see your doctor; some people need an injection form instead.

Calcium reduces absorption of iron, levothyroxine, some antibiotics (quinolones and tetracyclines) and bisphosphonates, so these are taken at different times; ask your pharmacist how far apart. Thiazide diuretics can raise calcium levels, so combining them with calcium or vitamin D needs monitoring. Orlistat, cholestyramine and other bile-acid binders, some anti-seizure medicines and long-term steroids reduce vitamin D levels or its effect. Acid-reducing medicines reduce absorption of calcium carbonate (citrate is better). Digoxin and calcium can be dangerous together if calcium rises. Check with your doctor before using high-dose supplements, especially if you have kidney disease, sarcoidosis, hyperparathyroidism or a history of kidney stones.

Vitamin D status is checked with a blood test for 25-hydroxyvitamin D (25-OH vitamin D), together with calcium, phosphate, kidney function, parathyroid hormone and sometimes alkaline phosphatase. Interpretation of the “normal” level differs between guidelines: many define deficiency as below 50 nmol/L (20 ng/mL), and some suggest higher targets in malabsorption or osteoporosis, so ask your doctor what your target is. Tests are usually repeated after about 3 months of treatment and then once or twice a year, more often if you have malabsorption or take high doses. A bone-density scan (DXA) is arranged for people at higher risk, such as those with coeliac disease, long-term steroid use, cirrhosis, cholestatic liver disease, short bowel or inflammatory bowel disease with other risk factors, and repeated at intervals chosen by your doctor.

Do not stop or restart on your own. In malabsorption conditions, supplements are often needed long term. In others, treatment may be reduced after levels normalise. Stop and contact your doctor if you develop symptoms of too much calcium or vitamin D.

Vitamin D and calcium needs are met safely in pregnancy and breastfeeding through food and standard supplements, and deficiency is treated because it affects mother and baby. Avoid high-dose supplements unless your doctor advises them, and keep preformed vitamin A low. Tell your obstetrician about gut or liver disease and any supplement you use.

Many studies in Saudi Arabia report that a large share of adults, women and older people have low vitamin D, even though the country is sunny, as fewer people spend time outdoors in the heat, many work indoors, clothing covers most skin, sunscreen is used, and skin pigmentation reduces vitamin D production. Because the pattern differs across studies and age groups, testing is better than guessing. Brief sensible sun exposure outside the hottest hours is helpful but should not mean sunburn, and it is not enough on its own for people with malabsorption. In Ramadan, vitamin D is best taken with iftar or suhoor meals containing some fat; weekly or other regimens may be used to simplify the schedule, but only as your doctor prescribes. Dairy such as laban and yoghurt, fish and eggs help, and many Saudi milks are fortified. Choose products registered with the SFDA and avoid unregulated imported or herbal bone remedies.

• Should I have my vitamin D, calcium and parathyroid hormone checked, and how often?

• Do I need a bone-density scan because of my gut or liver condition or my medicines?

• Which form and schedule of vitamin D and calcium suit me, and what is my target level?

• Does my acid-reducing medicine or steroid affect my bones, and what should I do about it?

• Are my other medicines affected by calcium, and when should I take each?

This guide comes from the Saudi Gastroenterology Association (SGA) patient library, prepared by the Approved for publication by SGA; individual clinician review is ongoing. Last reviewed: 2026-04-24. It is for education and does not replace your doctor's advice.