Quest Calcium 600 mg Plus Vitamin D

Our assessment

The evidence shows that calcium is essential for bone health, but it is not a supplement to take casually. Our assessment: you should approach calcium supplementation with a clear understanding of your own dietary intake and medical history. The data confirms that calcium supports bone mineralization and neuromuscular relaxation [NIH ODS]. However, the risks associated with high intake are significant and require careful management.

How it works

Think of calcium as a structural builder — it is deposited into your bone matrix to maintain density and strength. It also acts as a nerve signal regulator, helping muscles relax and nerves communicate properly [NIH ODS]. This dual role makes it critical, but also means that imbalances can affect both your skeleton and your heart function.

Safety profile

The FDA has received a total of 592,059 adverse event reports related to this product type [FDA data]. Specific risks from high calcium intake include constipation, nausea, weight loss, extreme tiredness, frequent urination, abnormal heart rhythms, poor muscle tone, and poor kidney function [NIH ODS]. Some research also suggests that high calcium intakes might increase the risk of heart disease and prostate cancer [NIH ODS]. Importantly, calcium can reduce the absorption of several medications, including bisphosphonates, tetracycline antibiotics, fluoroquinolone antibiotics, levothyroxine, and phenytoin [NIH ODS]. You should take calcium supplements at least two hours apart from these medications.

Our recommendation

Start by calculating your daily calcium intake from food. If you are already getting enough from dairy, fortified foods, or leafy greens, you likely do not need this supplement. If you do supplement, take it with food and spread doses throughout the day for better absorption. Do not exceed 500-600 mg of supplemental calcium at one time. Data not available on the exact vitamin D dosage in this product, so check the label carefully. Always consult your physician before starting, especially if you have a history of kidney stones, heart disease, or take any of the medications listed above [NIH ODS].

Supplement labels contain several key sections regulated by the FDA:

• Serving Size — The recommended amount per dose. Always check this — some products require multiple capsules per serving.
• Amount Per Serving — Shows the quantity of each nutrient in the product, typically in IU (International Units), mg (milligrams), or mcg (micrograms).
• % Daily Value (%DV) — Indicates how much a nutrient in a serving contributes to a daily diet. 5% DV or less is low; 20% DV or more is high.
• Other Ingredients — Lists inactive ingredients like fillers, binders, and capsule materials (e.g., gelatin, cellulose, magnesium stearate).
• Suggested Use — The manufacturer's recommended directions for taking the supplement, including timing and dosage.

Source: FDA Dietary Supplement Labeling Guide