Calcium and Bariatric Surgery

Calcium serves many vital functions and is our body’s most abundant mineral. This mineral is responsible for keeping teeth healthy and playing a role in blood clotting and muscle contraction, including the heart. Calcium is perhaps best known for making up much of the structure of our bones; in fact, 99% of the body’s calcium is stored in the bones. This is because our bodies use the bones as a reservoir for calcium to maintain homeostasis. While it isn’t damaging for our bodies to occasionally take calcium from bones, this can contribute to low bone density over time. Therefore, it’s essential to make sure we get enough calcium regularly.

Vitamin D helps the body absorb calcium, and this is why many calcium supplements also contain vitamin D and vice versa. The recommended daily intake (RDI) for calcium is about 1,000mg, though different populations need calcium in varying amounts. For example, the RDI for women over 51 is 1,200 mg daily, as women have a higher rate of bone loss after menopause. This is because estrogen enhances calcium absorption and decreases its excretion from the body. Also, as we age, our bodies produce less stomach acid, which hinders calcium absorption. Another factor impacting calcium needs is pregnancy or lactation; increasing calcium needs to 1200mg daily.

Since our bodies cannot produce calcium, we must get enough from our food. Many foods naturally contain calcium, and other foods are fortified with minerals added during processing. Dairy is well-known for being calcium-rich, with 1 cup of milk containing 300 mg of calcium. However, many other foods have substantial amounts of calcium, especially leafy greens. Eating a healthy, well-balanced diet is the best way to ensure you get enough calcium daily. Below are other sources of foods high in calcium:

  • 8oz plain Greek yogurt: 250mg
  • 3oz sardines: 325mg
  • ½ cup tofu: 250mg
  • 1 cup kale: 94mg
  • 1 cup canned black beans: 240mg

Specific diets can make it challenging to get enough calcium every day, most notably for vegans or those who are lactose intolerant. Fortified foods such as soy or almond milk, dry cereal, and orange juice can help. However, a supplement can otherwise help fill the gap.

A doctor, dietitian, or other health care provider may recommend a supplement depending on the medical status or nutritional needs. For example, bariatric surgery increases your calcium needs quite a bit. While most people need about 1,000 mg daily, a person who undergoes sleeve gastrectomy or Roux-en-Y gastric bypass needs about 1,200 to 1,500mg daily. After a duodenal switch, calcium needs may increase to about 1,800-2,400mg. This is because bariatric surgery reduces the size of the stomach, affecting the intake and absorption of many different nutrients. Since the body can only absorb about 500mg of calcium at a time, the supplements are often divided into three doses throughout the day. Another critical aspect of calcium intake is its effect on iron, as calcium has been shown to inhibit its absorption. For this reason, most healthcare providers recommend taking these supplements separately.

Since one of calcium’s main jobs is maintaining bone density, low intakes of this mineral can reduce bone strength and lead to osteoporosis, characterized by fragile, brittle bones and an increased risk of fracture. Severe calcium deficiency can also cause rickets in children, though this is more common with vitamin D deficiency. Signs of hypocalcemia, or severe calcium deficiency, include confusion and memory loss, muscle cramps, and spasms. In the United States, about 44% of the population is estimated not to meet the daily requirement for calcium. This may be due to low intakes of dairy and leafy greens, which can contribute to other nutrient deficiencies.

Calcium deficiency does not necessarily appear on a blood test since only 1% of the body’s calcium is in the blood. Therefore, a healthcare practitioner would likely recommend a supplement based on dietary intake and medical status. If calcium deficiency is a concern, a doctor may order a bone density test, referred to as a DEXA scan. This measures the amount of calcium and other minerals stored in bones and can also diagnose osteoporosis or osteopenia (an early sign of bone thinning). This can also occur when someone is underweight or malnourished.

Calcium is an essential nutrient for the body. Because most people don’t get enough calcium, eating a diet that includes lots of healthy foods every day, especially after bariatric surgery, is necessary. There are two leading calcium supplements: calcium carbonate (which is best absorbed with food) and calcium citrate (which can be taken either with or without food). Chewable vitamins are popular post-surgery as they are generally well-tolerated and easily absorbed than pill forms. Consuming too much calcium could be harmful, though this is not common. It’s important to review your vitamin and mineral levels with a dietitian and doctor, who can best determine your individual needs and come up with a specific plan.


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Chloe Seddon is a registered dietitian nutritionist who holds a Master’s Degree in health promotion from the University of Connecticut. She specializes in nutritional counseling, with a focus on a non-dieting approach to maintain healthy weight and goal-oriented lifestyle changes for long term success. She teaches intuitive eating and easy meal preparation to help clients sort through the myriad of nutritional misinformation to focus on having a balanced and happy relationship with food. She counsels clients with a range of issues, including chronic disease management, sports nutrition, disordered eating and weight loss. Chloe currently works as a nutritional counselor and educator providing group and individual consulting. She believes that balancing food, eating and exercise should be enjoyable and healthful.

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