After weight loss surgery, doctors usually watch for weak bones. But a new study found that about 1 in 11 patients actually have a different bone disease called osteomalacia that gets missed. This condition happens when your body can’t absorb enough vitamin D and calcium, making bones soft instead of just thin. The good news? Doctors can spot it by checking a simple blood test for an enzyme called alkaline phosphatase. If caught early, patients can get special high-dose vitamin D treatment to fix the problem instead of the usual osteoporosis treatment.

The Quick Take

  • What they studied: Whether patients who had weight loss surgery develop a specific bone-softening disease called osteomalacia, and how often doctors miss this diagnosis when they’re looking for regular weak bones.
  • Who participated: 46 people (mostly women, ages 42-77) who had weight loss surgery years ago and came to the hospital because doctors thought they had weak bones.
  • Key finding: About 9 out of 100 patients (4 out of 46) actually had osteomalacia instead of or along with weak bones. All of them had high levels of a blood enzyme called alkaline phosphatase, which is a red flag for this condition.
  • What it means for you: If you had weight loss surgery and are being treated for weak bones, ask your doctor to check your alkaline phosphatase levels. If it’s high, you might need different treatment—specifically high-dose vitamin D—rather than the standard weak bone treatment.

The Research Details

Researchers looked back at medical records of 46 people who had weight loss surgery and were sent to a bone specialist for weak bones. They checked everything in the patients’ files: what type of surgery they had, how long ago, what medicines they took, blood test results, X-rays, and bone density scans. They looked for signs of osteomalacia—a disease where bones become soft because the body can’t use calcium and vitamin D properly. The doctors used bone biopsies (tiny bone samples) and specific blood and imaging patterns to diagnose osteomalacia.

This type of study is called a ‘cohort study’ because researchers followed one group of people and looked back at their medical history. It’s like being a detective, looking through old case files to find clues. The study focused on patients from a rheumatology department (bone and joint specialists) in a hospital setting.

The researchers were trying to answer an important question: How many people with weight loss surgery actually have this hidden bone disease that doctors might mistake for regular weak bones?

Weight loss surgery can cause problems with how your body absorbs nutrients, especially calcium and vitamin D. These nutrients are super important for keeping bones strong. Most doctors know about weak bones after weight loss surgery, but osteomalacia is different—it’s about bones becoming soft, not just thin. If doctors treat osteomalacia like regular weak bones, patients won’t get the right medicine and their bones won’t heal properly. This study helps doctors learn to spot the difference by watching for a specific blood test result.

This study looked at a small group of 46 people, so the results might not apply to everyone. It’s also a ’look-back’ study, meaning researchers checked old medical records rather than following people forward in time. The study was done in one hospital department, so results might be different in other places. However, the findings are clear and specific—doctors found a real pattern that could help catch this disease earlier in other patients.

What the Results Show

Out of 46 patients who came in for weak bones, 4 patients (about 9%) actually had osteomalacia. Three of these four were women. Most had a specific type of weight loss surgery called ‘malabsorptive surgery’ (surgery that makes it harder for your body to absorb nutrients) done 4 to 13 years before the study.

All four patients with osteomalacia had very high levels of an enzyme called alkaline phosphatase in their blood. This was the most reliable warning sign. Most also had low calcium levels and low vitamin D levels. When doctors looked at their X-rays, the bones showed a pattern typical of osteomalacia—not just thin bones, but soft, weak bones.

Interestingly, all four patients also had osteoporosis (weak bones) on their bone density scans. Three of them had already broken bones or developed pseudofractures (cracks that look like breaks). The important point: none of these patients were sent to the hospital because a doctor suspected osteomalacia. They all came in because someone thought they just had regular weak bones.

All four patients with osteomalacia had high parathyroid hormone levels. The parathyroid gland makes a hormone that controls calcium in your body, so when calcium is low, this hormone goes up. This is another clue that something is wrong with calcium and vitamin D absorption. The study also found that the type of weight loss surgery mattered—malabsorptive surgeries (which bypass part of the intestines) caused more problems than restrictive surgeries (which just make the stomach smaller). The longer someone had the surgery, the more likely they were to develop this problem.

Doctors have known for years that weight loss surgery can cause weak bones. But this is one of the first studies to specifically look at how often osteomalacia—the bone-softening disease—happens in these patients. Previous research focused mainly on osteoporosis. This study suggests that osteomalacia might be more common than doctors realize and is probably being missed because doctors aren’t specifically looking for it. The finding that alkaline phosphatase is a key warning sign is new and helpful information.

The study only looked at 46 people in one hospital, so the results might not apply to everyone who has weight loss surgery. The study looked backward at old medical records, which means some information might be missing or incomplete. The study didn’t include a comparison group of people without weight loss surgery, so we can’t be 100% sure the surgery caused the osteomalacia. Also, the study was done in a specialized bone clinic, so it might not represent all people with weight loss surgery—just those with bone problems.

The Bottom Line

If you had weight loss surgery: (1) Make sure your doctor checks your vitamin D and calcium levels regularly—this is important. (2) Ask your doctor to check your alkaline phosphatase blood level if you’re being treated for weak bones. (3) If your alkaline phosphatase is high, ask if you might have osteomalacia instead of just weak bones. (4) You may need high-dose vitamin D supplements or even vitamin D injections rather than standard weak bone treatment. These recommendations are based on this one study of a small group, so talk with your doctor about what’s right for you.

This matters most for people who had weight loss surgery, especially malabsorptive surgery (like gastric bypass), and who are being treated for weak bones. It’s also important for doctors who treat these patients. If you had restrictive surgery (like gastric banding) and have good calcium and vitamin D levels, your risk is lower. If you had weight loss surgery but have never had bone problems, you should still get regular bone checks but your immediate risk is lower.

If you start high-dose vitamin D treatment, it usually takes several weeks to months to see improvements in blood test results. Bone healing takes longer—usually 6 to 12 months to see real changes in bone strength. Some people feel better (less bone pain) within weeks, but the real bone improvement takes time. This is a long-term condition that needs ongoing monitoring and treatment.

Want to Apply This Research?

  • Track your vitamin D and calcium supplement intake daily, noting the dose and type. Also log any bone pain, muscle weakness, or fractures. Set monthly reminders to record your weight and any new symptoms.
  • Set up a daily reminder to take your vitamin D and calcium supplements at the same time each day. Use the app to log your supplements immediately after taking them to build the habit. If your doctor prescribes high-dose vitamin D, set alerts for injection appointments or prescription refills.
  • Use the app to track blood test results when you get them (alkaline phosphatase, vitamin D, calcium, parathyroid hormone levels). Create a chart to see trends over time. Log any new fractures, bone pain, or falls. Share this data with your doctor at each visit to help them adjust your treatment if needed.

This research describes a pattern found in one small group of patients and should not be used for self-diagnosis. If you have had weight loss surgery and are concerned about bone health, osteomalacia, or vitamin D deficiency, consult with your doctor or a bone specialist. Do not start, stop, or change any medications or supplements without medical guidance. High-dose vitamin D and calcium supplementation require medical supervision. This article is for educational purposes and does not replace professional medical advice.