Diabetes: Causes, Symptoms, and Treatments — The Ultimate Guide

Diabetes is one of those health conditions people think they understand until they have to live with it. Most of us know it has something to do with blood sugar. Fewer people know that diabetes is actually a family of disorders with different root causes, different timelines, and different treatment strategies.

This matters because the old, one-size-fits-all story is outdated. In 2026, we can treat diabetes more precisely than ever: we can screen earlier, personalize medications, use continuous glucose monitoring, and reduce the risk of heart and kidney complications with therapies that were not available a decade ago. At the same time, diabetes prevalence keeps climbing, especially where healthy food, preventive care, and medication access are hardest to get.

This guide covers causes, symptoms, diagnosis, treatment, myths, controversies, and future directions. It is written for smart non-specialists who want real evidence, not buzzwords.

Why Are More People Living With Diabetes Than Ever Before?

Short answer: population aging, urbanization, sedentary patterns, calorie-dense food environments, obesity, social inequities, and better detection all play a role. Long answer: diabetes is shaped by biology and by systems. That means prevention and treatment both have to happen at multiple levels.

The World Health Organization reports that the number of people living with diabetes rose from 200 million in 1990 to 830 million in 2022. In the U.S., the CDC National Diabetes Statistics Report (updated January 21, 2026) estimates 40.1 million people had diagnosed or undiagnosed diabetes in 2023, and 11.0 million were undiagnosed.

Metric	Latest Figure	Why It Matters	Source
People living with diabetes worldwide	830 million (2022)	Shows global scale and fast growth over decades	WHO Fact Sheet
People with diabetes in the U.S.	40.1 million (2023 estimate)	About 12.0% of the U.S. population	CDC National Diabetes Statistics Report
Undiagnosed diabetes in U.S. adults	11.0 million (27.6% of adults with diabetes)	Large hidden burden and delayed treatment	CDC National Diabetes Statistics Report
U.S. economic burden	$640 billion (2021)	Medical costs + productivity losses at national scale	CDC Diabetes Basics

Did You Know? Diabetes is not just a glucose problem. It is a major driver of kidney failure, vision loss, cardiovascular disease, and amputations if poorly managed over time.

Diabetes Is Not One Disease

Think of “diabetes” as an umbrella term. Under it are disorders that share high blood glucose but differ in mechanism.

Type	Core Cause	Typical Onset Pattern	Approximate Share	Main Treatment Approach
Type 1	Autoimmune destruction of insulin-producing beta cells	Often younger age, but can occur at any age	About 5% to 10% of diagnosed cases	Insulin replacement from diagnosis
Type 2	Insulin resistance plus progressive beta-cell dysfunction	Usually gradual, often years before diagnosis	About 90% to 95% of diagnosed cases	Lifestyle + medication, sometimes insulin
Gestational	Pregnancy-related insulin resistance	Detected during pregnancy	About 5% to 9% of U.S. pregnancies	Nutrition, activity, glucose monitoring, medications if needed
Other specific types	Genetic syndromes, pancreatic disease, medications, endocrine disorders	Varies	Smaller subset	Cause-specific + glucose management

Sources: CDC Diabetes Basics, CDC Risk Factors, and CDC gestational diabetes information.

What Actually Causes Blood Sugar to Rise?

Your body is running a constant fuel economy. Insulin is the key that allows glucose to move from blood into cells. In type 2 diabetes, two problems evolve together: cells become less responsive to insulin, and over time the pancreas cannot keep up with higher demand.

Why does this happen? There is no single trigger. Genetics increase susceptibility; body fat distribution matters; liver fat and muscle insulin resistance matter; sleep disruption, stress, and inactivity contribute; and social factors shape food, movement, and healthcare access. For type 1 diabetes, the mechanism is autoimmune and not caused by eating sugar.

A Brief History of How We Got Here

• 1921–1922: Insulin is discovered and first used clinically, transforming type 1 diabetes from rapidly fatal to manageable.
• Late 20th century: Home glucose meters and A1C standardization improve self-management.
• 1993 and 1998: Landmark trials show that better glycemic control reduces microvascular complications (DCCT; UKPDS 33).
• 2015 onward: Outcome trials show some glucose-lowering drugs protect heart and kidney outcomes, not just glucose numbers (EMPA-REG, LEADER, CREDENCE, DAPA-CKD).

One in Four U.S. Adults With Diabetes May Not Know They Have It

Diabetes can be quiet for years. Many people feel “mostly normal” until routine labs reveal elevated A1C, fasting glucose, or oral glucose tolerance test abnormalities. That is why relying on symptoms alone is risky.

Common Symptoms

• Frequent urination
• Excessive thirst
• Fatigue
• Blurred vision
• Slow-healing cuts
• Frequent infections
• Unintentional weight loss (more common in type 1 and advanced hyperglycemia)

Red Flags That Need Urgent Care

• Nausea, vomiting, abdominal pain, deep breathing, confusion, fruity breath (possible diabetic ketoacidosis)
• Severe dehydration, confusion, extreme high glucose in older adults (possible hyperosmolar crisis)

Quick Fact: The CDC estimates that more than 1 in 4 U.S. adults with diabetes may be undiagnosed, which is why risk-based screening is crucial even when people feel well.

How Is Diabetes Diagnosed, and Who Should Be Screened?

Diagnosis is based on blood tests, not guesswork. The CDC testing guidance and major guidelines align on these thresholds:

Test	Normal	Prediabetes	Diabetes
A1C	<5.7%	5.7% to 6.4%	≥6.5%
Fasting Plasma Glucose	<100 mg/dL	100 to 125 mg/dL	≥126 mg/dL
2-hour OGTT (75 g glucose load)	<140 mg/dL	140 to 199 mg/dL	≥200 mg/dL

The USPSTF 2021 recommendation advises screening nonpregnant adults age 35 to 70 who have overweight or obesity, and referring people with prediabetes to effective preventive interventions. Pregnancy screening for gestational diabetes is typically done at 24 to 28 weeks, with earlier screening in higher-risk pregnancies (CDC guidance).

Did You Know? A1C is useful but not perfect. Conditions like anemia, kidney disease, or some hemoglobin disorders can affect A1C accuracy, so clinicians may pair it with other tests.

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Maria Felt Fine Until a Routine Test Changed Everything

Imagine this common scenario: Maria is 44, works full time, sleeps poorly, and feels tired but assumes it is stress. Her annual checkup shows A1C of 6.1% (prediabetes). She has no dramatic symptoms, so she is shocked. This is exactly where prevention can work best.

The strongest prevention data still come from the Diabetes Prevention Program trial in NEJM (Knowler et al., 2002). In high-risk adults, intensive lifestyle intervention reduced progression to type 2 diabetes by 58%, while metformin reduced it by 31%, versus placebo over about 3 years.

What Lifestyle Intervention Actually Meant in That Trial

• Moderate weight loss target
• Regular physical activity goal
• Structured coaching and follow-up
• Behavior change support, not just advice handouts

That last point is underappreciated. Telling people to “eat better” is weak medicine. Structured programs with coaching and accountability are stronger medicine.

TL;DR: Prediabetes is not a cosmetic diagnosis. It is a measurable risk state where intervention can prevent years of future disease burden.

"Treat the Person, Not Just the Glucose Number"

Modern diabetes care is person-centered and outcome-centered. A1C still matters, but it is no longer the only metric. Clinicians now consider cardiovascular risk, kidney function, hypoglycemia risk, body weight, cost, access, and patient preferences in treatment decisions.

Older Model	Current Model
Glucose-only focus	Glucose + heart + kidney + quality-of-life outcomes
Stepwise escalation with long delays	Earlier combination strategy for high-risk profiles
Medication class chosen mainly by A1C reduction	Medication class chosen by outcome evidence, comorbidities, and access
Limited glucose data between clinic visits	Continuous or frequent data via CGM and connected tools

Nutrition remains central, but there is no universal “best diet.” Evidence supports multiple patterns when adherence is good: Mediterranean-style, lower-carbohydrate, and high-fiber approaches can all improve glycemia and cardiometabolic risk (Goldenberg et al., BMJ, 2021; Evert et al., Diabetes Care, 2019).

A 0.5% A1C Drop Can Be Meaningful, but Heart and Kidney Outcomes Matter More

Medication choice has become more sophisticated because outcome trials changed the field.

Medication Class	Typical A1C Effect	Weight Effect	Outcome Signals	Key Considerations
Metformin	Moderate	Neutral to slight loss	Long track record, low cost	GI effects, adjust/avoid in advanced kidney dysfunction
SGLT2 inhibitors	Modest	Loss	Cardiorenal benefit in multiple trials	Genital infections, volume effects, ketoacidosis risk in select contexts
GLP-1 receptor agonists	Moderate to high	Loss	MACE reduction in several cardiovascular outcome trials	GI effects, cost/access barriers, titration needed
Insulin	High	Can increase	Essential in type 1 and many with type 2	Hypoglycemia risk, dosing complexity, monitoring burden

Examples of outcome evidence:

• EMPA-REG OUTCOME (NEJM, 2015): empagliflozin reduced major cardiovascular events and lowered cardiovascular death and heart failure hospitalization in high-risk type 2 diabetes.
• LEADER (NEJM, 2016): liraglutide reduced major cardiovascular events.
• SUSTAIN-6 (NEJM, 2016): semaglutide reduced major cardiovascular events in high-risk populations.
• CREDENCE (NEJM, 2019): canagliflozin significantly reduced risk of kidney and cardiovascular outcomes in diabetic nephropathy.
• DAPA-CKD (NEJM, 2020): dapagliflozin reduced kidney failure progression and death in CKD populations, including people with diabetes.

Guideline synthesis from nephrology also reflects this shift toward cardiorenal protection-first approaches in high-risk patients (KDIGO 2022 executive summary).

Quick Fact: In current practice, “best diabetes medication” often means “best medication for this person’s heart, kidneys, glucose, and daily life,” not just the biggest A1C drop.

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The Quiet Damage: Eyes, Kidneys, Nerves, Heart, and Brain

Chronically elevated glucose damages blood vessels and nerves. The endpoints are not abstract: vision loss, neuropathic pain, kidney failure, heart attacks, strokes, and amputations.

Classic trials proved that better glycemic control reduces microvascular injury. In type 1 diabetes, DCCT showed large reductions in retinopathy and nephropathy progression. In type 2 diabetes, UKPDS 33 showed significant microvascular benefit from more intensive control.

Practical Monitoring Checklist

• Regular A1C and home/CGM glucose review
• Annual urine albumin and kidney function checks
• Dilated eye exams at guideline-recommended intervals
• Routine foot exams and daily self-checks for wounds
• Blood pressure and lipids managed aggressively
• Vaccinations, smoking cessation, and sleep/mental-health support

Myths Keep People Sicker for Longer

Myth	Fact
“Type 2 is just from eating too much sugar.”	Diet matters, but genetics, insulin resistance biology, sleep, stress, adiposity, medications, and social environment all contribute.
“If I start insulin, I failed.”	Insulin is a tool, not a moral grade. For type 1 it is life-sustaining; for type 2 it can be essential at specific disease stages.
“No symptoms means no problem.”	Diabetes and prediabetes can be silent for years; screening catches risk before irreversible damage.
“New drugs are only about weight loss.”	Some newer agents have proven cardiovascular and kidney benefits independent of glucose lowering alone.
“Once glucose improves, complications are off the table.”	Risk falls but does not instantly disappear; prevention is ongoing and cumulative.
“Diabetes care is just medical.”	Food security, housing, affordability, and mental health profoundly affect outcomes.

Can Type 2 Diabetes Go Into Remission?

Yes, for some people. But remission is not guaranteed, not permanent for everyone, and not equivalent to “cure.”

The DiRECT trial (Lancet, 2018) showed substantial remission rates with intensive weight-management in primary care. The strongest remission rates were seen in those with greater weight loss, especially early after diagnosis. Surgical evidence is also strong: the STAMPEDE 5-year outcomes (NEJM, 2017) showed bariatric/metabolic surgery plus medical therapy outperformed medical therapy alone for glycemic targets in selected patients.

Counterpoint: remission narratives can unintentionally shame people who do not achieve it. Biology varies. Disease duration varies. Medication access varies. Clinically, success should be defined as risk reduction and quality of life, not a single binary label.

Did You Know? Remission is most likely when intervention happens earlier in type 2 diabetes and is sustained with long-term follow-up support.

Technology Is Turning Diabetes Care Into Real-Time Decision-Making

The old model was occasional glucose snapshots. The new model is trend-based management. Continuous glucose monitoring (CGM) gives patterns, alarms, and “time in range” insights that fingersticks alone cannot provide.

A systematic review and network meta-analysis found CGM improved glycemic metrics in type 2 diabetes compared with traditional self-monitoring, including better A1C and time-in-range outcomes (Park et al., Diabetes Obes Metab, 2023).

On the device side, the FDA expanded automated insulin-dosing technology to include type 2 diabetes on August 26, 2024 (FDA press announcement), signaling broader acceptance of algorithm-assisted care beyond type 1.

What Could Diabetes Care Look Like in 2035?

Three frontiers are moving fast: prevention immunology, biologic/cellular therapies, and access innovation.

1) Delaying Type 1 Before It Starts

Regulators approved teplizumab (TZIELD) for delaying stage 3 type 1 diabetes on November 17, 2022, a major conceptual shift from reaction to prevention in high-risk individuals (FDA Drug Trials Snapshot).

2) Cell-Based and Advanced Biological Approaches

Research and approvals in islet-cell and related biologic strategies suggest a future where selected people with brittle type 1 diabetes may have additional options beyond standard insulin-only pathways (FDA announcements, 2023 onward).

3) Affordability and Supply-Side Changes

On February 14, 2025, the FDA approved the first rapid-acting insulin biosimilar in the U.S. (FDA press announcement). Biosimilar competition may improve access over time, though pricing and coverage policy remain decisive.

Future outlook, realistically: we are more likely to see better lifelong control, fewer complications, and more delayed-onset disease than a single universal cure in the near term.

Earlier Action Beats Perfect Action

If you remember one thing, make it this: diabetes outcomes are path-dependent. The earlier you detect risk and intervene, the better the long-term trajectory.

1. Know your numbers: A1C, fasting glucose, blood pressure, lipids, kidney markers.
2. If eligible, get screened on schedule, even without symptoms.
3. Treat prediabetes as actionable, not optional.
4. Choose therapies based on total risk profile, not hype cycles.
5. Use technology when it reduces burden and improves decisions.
6. Address mental health and social barriers as core clinical factors.
7. Track progress over months and years, not just one lab day.

Diabetes management is not about perfection. It is about consistent, evidence-based course correction.

Selected Evidence and Guidelines

• WHO Diabetes Fact Sheet (updated November 14, 2024)
• CDC National Diabetes Statistics Report (updated January 21, 2026)
• CDC Diabetes Testing
• CDC Diabetes Risk Factors
• USPSTF Screening Recommendation (JAMA, 2021)
• Knowler et al., NEJM, 2002 (DPP)
• DCCT Research Group, NEJM, 1993
• UKPDS Group, Lancet, 1998
• Zinman et al., NEJM, 2015 (EMPA-REG)
• Marso et al., NEJM, 2016 (LEADER)
• Marso et al., NEJM, 2016 (SUSTAIN-6)
• Perkovic et al., NEJM, 2019 (CREDENCE)
• Heerspink et al., NEJM, 2020 (DAPA-CKD)
• Lean et al., Lancet, 2018 (DiRECT)
• Schauer et al., NEJM, 2017 (STAMPEDE 5-year)
• Park et al., Diabetes Obes Metab, 2023 (CGM meta-analysis)
• KDIGO 2022 Executive Summary
• FDA TZIELD Drug Trials Snapshot
• FDA automated insulin dosing in type 2 (August 26, 2024)
• FDA rapid-acting insulin biosimilar approval (February 14, 2025)