What is the best calcium supplement for optimal absorption?

From the Guidelines

Calcium citrate is generally considered the best calcium supplement for optimal absorption. It can be taken with or without food, making it more convenient and effective for most people, especially those who have undergone bariatric surgery, as noted in the British Obesity and Metabolic Surgery Society guidelines 1. A typical dose is 500-600 mg of elemental calcium taken twice daily for a total of 1000-1200 mg per day, although the optimal calcium intake for people who have had bariatric surgery is recommended to be 1200- to 1500-mg calcium per day from food and supplements following certain procedures, and 1800–2400 mg d−1 following others 1. Some key points to consider when choosing a calcium supplement include:

• Calcium citrate is better absorbed than calcium carbonate, which requires stomach acid for proper absorption and should be taken with meals 1.
• Calcium citrate may be more bioavailable and the preferred option for people at risk of kidney stones, but calcium carbonate may be better tolerated 1.
• It's recommended to take calcium in divided doses, taking calcium carbonate with meals and calcium citrate with or without meals 1.
• Good hydration should be encouraged to minimize the risk of kidney stones 1.
• Vitamin D supplementation is also crucial, with recommended starting regimens of 2000–4000 IU of vitamin D3 per day to maintain serum 25OHD levels after surgery 1. It's essential to consult with a healthcare provider before starting any calcium supplement, especially if you have kidney disease or a history of kidney stones.

From the FDA Drug Label

The FDA drug label does not answer the question.

From the Research

Forms of Calcium Supplements

• Calcium carbonate and calcium citrate are the most common forms of calcium supplements 2
• Calcium carbonate is the most cost-effective form, but should be taken with a meal to ensure optimal absorption 2
• Calcium citrate can be taken without food and is the supplement of choice for individuals with achlorhydria or who are taking histamine-2 blockers or protein-pump inhibitors 2
• Calcium lactate and calcium gluconate are less concentrated forms of calcium and are not practical oral supplements 2
• Hydroxyapatite as a source of calcium is not recommended due to limited research 2

Factors Affecting Absorption

• Gastric acid is not necessary for absorption of calcium supplements, as long as they are taken with meals 3
• A divided dose regimen (4x/d; i.e., with meals and at bedtime) results in substantially greater absorption of a supplement than does 1x/d dosing 3
• The intestinal absorption of calcium citrate is approximately 24% better than that of calcium carbonate, independent of intake with meals 4

Recommended Dosage

• The maximum dose of elemental calcium that should be taken at a time is 500 mg 2
• Daily supplementation with 500 mg of calcium is usually required to achieve a total intake of 1,200 mg 4
• Calcium supplementation should be tailored to the patient's need, based on total daily dietary calcium intake 4

Combination with Vitamin D

• The combination of calcium with vitamin D forms the basis of preventive and therapeutic regimens for osteoporosis 5
• A number of studies have suggested that the combination of calcium and vitamin D is effective when administered at respective dosages of at least 1200 mg and 800 IU per day 5
• Daily supplementation with 800 IU of vitamin D is a practical and safe strategy without the need for prior determination of vitamin D levels 4