Blood Alcohol Content (BAC)
Definition
The concentration of alcohol in the bloodstream, expressed as a percentage or g/dL.
Example: 0.08% BAC = 0.08 grams of alcohol per 100 mL of blood.
Why It Matters
BAC has significant safety and health implications: - Legal limits - Driving limits in most jurisdictions - Impairment assessment - Cognitive and motor effects - Safety decisions - When safe to drive or operate machinery - Health tracking - Alcohol consumption patterns - Medical relevance - Affects medication interactions, health conditions
How It's Measured
- Breathalyzers - Estimate BAC from breath alcohol
- Blood tests - Direct measurement (clinical/legal)
- Estimation apps - Calculate based on drinks, weight, time
- Smart devices - Some wearables estimate BAC
HealthKit data: Typically from estimation apps or connected breathalyzers.
Reference Levels
| BAC | Effects |
|---|---|
| 0.02% | Relaxation, slight mood change |
| 0.05% | Lowered alertness, impaired judgment |
| 0.08% | Legal limit in many jurisdictions; reduced coordination |
| 0.10% | Clear impairment of coordination and judgment |
| 0.15% | Significant impairment, difficulty walking |
| 0.20% | Confusion, nausea, possible blackout |
| 0.30% | Stupor, unconsciousness possible |
| 0.40%+ | Potentially fatal |
Confounders & Limitations
- Individual variation - Body weight, metabolism, tolerance
- Food intake - Eating slows absorption
- Time course - BAC rises and falls over hours
- Device accuracy - Consumer breathalyzers vary in precision
- Estimation errors - Apps provide rough estimates only
Factors Affecting BAC
- Body weight - Lower weight = higher BAC per drink
- Biological sex - Women typically reach higher BAC
- Rate of consumption - Faster drinking = higher peak
- Food - Eating slows absorption
- Carbonation - May speed absorption
- Medications - Interactions with some drugs
Use Cases
- Safety decisions - When safe to drive
- Consumption tracking - Monitoring alcohol intake
- Health awareness - Understanding alcohol effects
- Event planning - Responsible drinking
Important Notes
- Legal BAC limits vary by jurisdiction
- Even below legal limits, impairment occurs
- No amount of alcohol is "safe" for driving
- "Sobering up" only happens with time—coffee/food don't speed it