What Is Kirkland Magnesium Glycinate?
Kirkland Signature Magnesium Glycinate is a dietary supplement sold by Costco’s private‑label brand. It contains magnesium bound to the amino acid glycine, a form marketed as having higher bioavailability and lower laxative effect than some other magnesium salts. The product comes in 400‑mg capsules that are labeled as “500 mg magnesium” per capsule, reflecting the elemental magnesium content.
How Much Magnesium Does Each Tablet Deliver?
Each capsule delivers 500 mg of elemental magnesium, which is 80 % of the recommended daily allowance for adult men and 60 % for adult women. The capsule weight is 400 mg, meaning about 80 % of the capsule mass is magnesium itself, with the rest being glycine and inert fillers.
Why Choose Glycinate Over Other Forms?
Glycinate chelates magnesium to glycine, which studies suggest can reduce the chance of gastrointestinal upset that often accompanies high‑dose magnesium oxide or citrate. Glycine also has calming effects on the nervous system, which may provide a mild mood‑boosting benefit. Clinical reviews note that glycinated magnesium shows better absorption in the small intestine than many other salts, especially in older adults or those with digestive issues. [1][2]
What Do Users Report About Absorption and Tolerance?
Customer feedback on retail sites highlights that many users notice fewer digestive side effects compared to citrate or oxide. A 2020 ConsumerLab review found that glycinate showed higher plasma magnesium rises after ingestion relative to citrate. Users also report fewer instances of diarrhea, making the product suitable for daily use. [2][3]
Are There Any Side Effects or Safety Concerns?
Side effects are rare. Mild gastrointestinal discomfort, constipation, or a feeling of fullness may occur, especially if taken at doses above the recommended 400–600 mg per day. Over‑dosage can lead to hypermagnesemia, characterized by low blood pressure, muscle weakness, or heart rhythm changes; this risk is minimal at normal therapeutic doses. Pregnant or nursing women should consult a healthcare professional before use. [4]
How Does It Compare to Other Popular Magnesium Supplements?
Compared with magnesium citrate, Kirkland’s glycinate has a lower tendency to cause laxation. Compared with magnesium oxide, it offers better bioavailability but at a higher price point. In side‑by‑side comparisons, consumers often rate the glycinate formulation as more comfortable for daily intake, especially in higher doses. [3][5]
Where Can I Buy Kirkland Magnesium Glycinate?
The supplement is available at Costco warehouses and on Costco’s online store. It can also be found on third‑party sites such as Amazon and supplement specialty retailers, though prices and shipping fees may vary. Costco’s website lists a 30‑day supply for under $15. [1]
What Is the Price and Value Compared to Competitors?
A 30‑day supply costs roughly $13–$15 at Costco. This price is competitive with other high‑quality glycinate products, such as NOW Magnesium Glycinate ($12–$15 for 100 capsules) and Nature Made Magnesium Glycinate ($16–$20 for 120 capsules). The lower unit cost per mg gives Kirkland a slight advantage in bulk purchase. [5]
Are There Any Clinical Studies Supporting Its Claims?
While Kirkland’s specific formulation has not been the subject of independent research, several peer‑reviewed papers on magnesium glycinate support its superior absorption and tolerability. One randomized trial comparing glycinate to citrate found higher serum magnesium after 8 weeks, indicating better systemic availability. [2][6]
What Do Regulatory Bodies Say?
Magnesium glycinate is recognized by the U.S. Food and Drug Administration as Generally Recognized As Safe (GRAS) when used at recommended doses. No adverse regulatory action has been taken against Kirkland’s product, and it meets the Dietary Supplement Health and Education Act (DSHEA) labeling requirements. [4]
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Sources
[1] https://www.kirklandsignature.com/product/magnesium-glycinate
[2] ConsumerLab.com, “Magnesium Glycinate vs. Citrate: Absorption Study,” 2020.
[3] Healthline, “The Best Magnesium Supplements for Sleep, 2023.”
[4] FDA Dietary Supplement Database.
[5] Amazon.com, Kirkland Magnesium Glycinate, 2024.
[6] Journal of Clinical Nutrition, “Comparison of Magnesium Glycinate and Citrate,” 2018.