2. Medication and Flare-Ups Can Affect Calcium AbsorptionPeople with Crohn’s disease may run low in calcium, in part because many with the condition are also likely to be lactose intolerant. (If you’re lactose intolerant, you may have to avoid dairy, which is rich in calcium.) Some drugs, such as corticosteroids, can affect calcium absorption, too.A flare-up of Crohn’s can also cause lower levels of albumin — a protein made by the liver that binds to calcium — and lead to lower calcium levels.Calcium is essential for making and sustaining bone, as well as keeping the heart and muscles working properly. This means people with Crohn’s can be at risk of osteoporosis, bone fractures, weak muscles, and irregular heart rhythms.“The trick is to not restrict your diet too much or avoid dairy products,” says Sandborn. “But, if dairy is exacerbating your Crohn’s symptoms, then over-the-counter calcium supplements are good.”Treating the flare-up with biologic drugs can help ease the inflammation, which may also restore levels of albumin and help correct calcium levels.3. Resection Surgery Can Make It Hard to Absorb Vitamin B12Vitamin B12 is the most common deficiency among people with Crohn’s, says Sandborn. Severe cases can lead to nerve damage, resulting in tingling or numbness in the fingers and toes.Vitamin B12 is absorbed in the ileum, the lower portion of the small intestine that leads to the large intestine. If the end portion of the ileum has been inflamed, scarred, or surgically removed (as happens in people with Crohn’s), the vitamin does not properly absorb in the body, which results in a deficiency.Like iron, this vitamin is important for maintaining a sufficient level of red blood cells.“Your doctor needs to periodically monitor vitamin B12 in your blood,” says Sandborn. “Patients will typically need lifetime replacement if they’ve had corrective surgery for Crohn’s.”B12 is mostly found in animal products, such as eggs, milk, fish, poultry, and other meats. Fortified breakfast cereals can also provide sufficient vitamin B12. But, if the end portion of the ileum has been removed, Sandborn explains that the vitamin will have to be given as a shot (typically once a month) or an intranasal formulation, such as a nasal spray.4. Lack of Folic Acid in the Diet Causes Folate-Deficiency AnemiaFolate deficiency is less common among people with Crohn’s and occurs most often in those taking methotrexate or sulfasalazine. When inflammatory bowel disease specialists prescribe either of these drugs, they often also prescribe a folic acid supplement to compensate for folate loss.Folate is a B complex vitamin, found in beans, leafy green vegetables, asparagus, rice, and fruits. It is key to producing red blood cells for protein synthesis and skin health. A deficiency can result in skin inflammation or dermatitis.Pregnant women, including women with Crohn’s, are advised to take folic acid to prevent birth defects.5. Insufficient Vitamin D Can Trigger Flare-UpsVitamin D deficiency is very common in people with Crohn’s. “Just having Crohn’s seems to be an additional risk factor for vitamin D deficiency, but it’s not well understood why,” says Sandborn.The two main ways to get vitamin D are with sunlight and a supplement. (Vitamin D is also found in certain foods, including eggs, fortified milk, fatty fish, and butter, but not in levels high enough for optimal health.)Vitamin D is essential for bone health, and a review published in 2019 in Frontline Gastroenterology found that flares create a high risk of vitamin D deficiency, but maintaining vitamin D levels reduces the risk of flares.Talk to your doctor if you’re concerned about vitamin D deficiency, so they can run tests and determine your current levels.“There is still a lot of research to be done in Crohn’s disease,” Sandborn says. “[Following a] restricted diet is a common practice, but I think this does a lot of harm, because there’s not enough science behind some of these restrictions. Many patients don’t need so many restrictions. Eating a healthy, well-balanced diet is probably the best thing you can do.”