French Study: Magnesium Levels May Boost Jardiance Benefits in Heart Failure

A Study from France Reveals Magnesium's Hidden Role in Heart Failure Treatment

A study from France, published in JACC: Heart Failure (2026), uncovers a surprising connection between magnesium levels in the blood and how well the popular diabetes and heart failure medication empagliflozin (Jardiance) works. Conducted using data from the large international EMPEROR-Reduced trial, this research could change how doctors monitor and treat American patients living with both diabetes and heart failure.

What the Researchers Did

Scientists analyzed blood magnesium levels in 3,730 patients with heart failure with reduced ejection fraction (HFrEF) — a condition where the heart muscle doesn't pump blood as well as it should. Patients were randomly assigned to receive either 10 mg/day of empagliflozin or a placebo and were followed for a median of 16 months. Researchers tracked cardiovascular deaths, heart failure hospitalizations, and kidney outcomes while measuring magnesium levels at multiple points throughout the study.

Key Findings — With US Unit Conversions

The average baseline magnesium level was 2.02 mg/dL (converted from 0.83 mmol/L). Patients were divided into five groups (quintiles) by magnesium level:

• Lowest group (Q1): ~1.65 mg/dL — patients here had diabetes more frequently
• Highest group (Q5): ~2.36 mg/dL — patients tended to be older with reduced kidney function

For reference, normal serum magnesium in US labs typically ranges from 1.7–2.4 mg/dL, meaning many heart failure patients in Q1 were at or below the lower boundary of normal.

The headline finding: empagliflozin reduced the risk of cardiovascular death or heart failure hospitalization by 46% in the lowest magnesium group (Q1), compared to a much smaller, statistically insignificant benefit in patients with normal-to-high magnesium. Additionally, empagliflozin raised magnesium levels by approximately 0.12 mg/dL (0.05 mmol/L) — a modest but meaningful increase.

Why This Matters for US Patients

Magnesium deficiency is extremely common in the United States, particularly among people with Type 2 diabetes — estimates suggest 25–38% of diabetic patients have low magnesium. Poor diet, diuretic medications (commonly prescribed for heart failure), and diabetes-related kidney changes all deplete magnesium. Yet routine magnesium testing is not a standard part of most American diabetes or heart failure management protocols.

This French research suggests that if you have diabetes and heart failure, your magnesium level may predict how much benefit you'll get from Jardiance — one of the most widely prescribed medications in its class. The American Diabetes Association (ADA) currently recommends empagliflozin for patients with Type 2 diabetes and established heart failure, but existing US guidelines do not yet address magnesium monitoring as part of this treatment decision.

Patients taking diuretics like furosemide (Lasix) should speak with their doctor about whether a simple, low-cost magnesium blood test makes sense for them — especially before or after starting empagliflozin.

The Bottom Line

This research adds an important piece to the puzzle of personalized diabetes and heart failure care. Checking magnesium levels may help identify which patients stand to gain the most from empagliflozin — and the drug itself may help correct a common deficiency at the same time.

Source: Ferreira, Anker, Butler et al. "Serum Magnesium and the Effect of Empagliflozin in Heart Failure With Reduced Ejection Fraction: Findings From EMPEROR-Reduced." JACC: Heart Failure, 2026. DOI: 10.1016/j.jchf.2025.102751. PMID: 41171249.