Quest Synergistic Iron 25 mg

Our assessment

The evidence shows that Quest Synergistic Iron 25 mg contains 25 mg of iron per serving, but data on the specific formulation and its synergistic ingredients is not available. The primary ingredient we have data on is calcium, not iron, so our assessment must focus on what the data provides. For general bone and nerve health, calcium is well-supported, but the product label indicates iron is the main ingredient. Data not available for the iron content or its specific effects in this product.

How it works

If this product were a calcium supplement, it would work by supporting bone mineralization and neuromuscular relaxation. Calcium helps deposit minerals into your bone matrix for density and helps your muscles relax and nerves signal properly [NIH ODS]. However, since the product is labeled as iron, the mechanism of action for iron—such as oxygen transport in red blood cells—is not covered by the provided data.

Safety profile

FDA received 592,059 total adverse event reports for supplements in this category. For calcium specifically, some research suggests that high intakes might increase the risk of heart disease and prostate cancer [NIH ODS]. High levels of calcium in the blood and urine can cause poor muscle tone, poor kidney function, low phosphate levels, constipation, nausea, weight loss, extreme tiredness, frequent need to urinate, abnormal heart rhythms, and a high risk of death from heart disease [NIH ODS]. Side effect report counts for this specific product are not available.

Our recommendation

We recommend you consult your healthcare provider before starting this supplement, as the data does not provide specific information on the synergistic iron formulation. If you are seeking iron supplementation, have your iron levels tested first to determine if you have a deficiency. For calcium, if that is your goal, take it separately from medications like bisphosphonates, tetracycline antibiotics, fluoroquinolone antibiotics, levothyroxine, and phenytoin, as calcium can reduce their absorption [NIH ODS]. Data not available for a final recommendation on this specific product.

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