Japan Study: Dapagliflozin Boosts Type 1 Diabetes Control for a Full Year

A study from Japan has found that dapagliflozin (brand name Farxiga) — a medication originally developed for Type 2 diabetes — can meaningfully improve long-term blood sugar control when added to insulin therapy in people living with Type 1 diabetes. The 52-week findings, drawn from Japanese participants in the global DEPICT-2 clinical trial, offer encouraging news for Type 1 patients who struggle to reach their A1C goals on insulin alone.

What the Japanese Researchers Found

Researchers at Kumamoto University studied 154 Japanese adults with Type 1 diabetes. Participants were randomly assigned to receive either dapagliflozin 5 mg, dapagliflozin 10 mg, or a placebo — all in addition to their usual insulin regimen. After 24 weeks, both dapagliflozin doses had meaningfully lowered A1C compared to placebo: by 0.58% in the 5 mg group and 0.80% in the 10 mg group. Critically, these improvements held steady all the way through the full 52-week study period.

Beyond A1C, both doses also:

• Reduced body weight — a common concern for insulin-dependent patients who often experience weight gain
• Lowered total daily insulin dose — meaning patients needed less insulin to manage their blood sugar
• Reduced glucose variability as measured by continuous glucose monitors (CGM), suggesting more stable, predictable blood sugar levels throughout the day
• Increased the proportion of patients achieving an A1C reduction of 0.5% or more without experiencing severe low blood sugar (hypoglycemia)

Understanding the Numbers in US Terms

While the study reported outcomes primarily in A1C percentages — which are already standard in the US — it's worth noting that glucose variability improvements measured by CGM align with American Diabetes Association (ADA) goals of keeping blood sugar between 70–180 mg/dL (3.9–10.0 mmol/L) for more than 70% of the day. Better glucose stability directly supports that target.

The Safety Warning You Need to Know

The study did identify a serious risk: diabetic ketoacidosis (DKA) occurred in patients taking dapagliflozin — one case in the 5 mg group and two cases in the 10 mg group — but in none of the placebo patients. DKA is a potentially life-threatening condition. This mirrors safety signals seen in US clinical data, which is why the FDA requires a black box warning about DKA risk when SGLT2 inhibitors are used in Type 1 diabetes.

Why This Matters for US Patients

The FDA approved dapagliflozin as an adjunct to insulin for Type 1 diabetes in 2019, though its use remains carefully monitored. What makes this Japanese study particularly valuable for American patients is the consistency of its results across a genetically and clinically distinct population. Japanese patients with Type 1 diabetes tend to have lower average body weight and different insulin sensitivity profiles than typical US patients — yet the benefits and risks of dapagliflozin were nearly identical. This cross-population consistency strengthens confidence that the drug's profile holds up broadly.

For US patients with Type 1 diabetes who are not meeting A1C goals on insulin alone, or who are concerned about weight gain and rising insulin doses, this research supports a conversation with your endocrinologist about whether an SGLT2 inhibitor like dapagliflozin might be appropriate — with close monitoring for DKA risk.

Always consult your diabetes care team before making any changes to your treatment plan.

Original Study Citation

Araki E, Mathieu C, Shiraiwa T, et al. Long-term (52-week) efficacy and safety of dapagliflozin as an adjunct to insulin therapy in Japanese patients with type 1 diabetes: Subgroup analysis of the DEPICT-2 study. Diabetes, Obesity & Metabolism. 2021. DOI: 10.1111/dom.14362. PMID: 33620762.