5.2 Effects of Alcohol: Age, Gender & BAC

Why Two Patrons Drinking the Same Amount Present Differently

A common mistake in licensed premises is judging intoxication by counting drinks. Two patrons can each consume three standard drinks and one is visibly affected while the other shows no signs. The duty manager's legal test is the individual's observable signs, not the drink count, and this section explains the physiology behind that variation.

The New Zealand Standard Drink

In New Zealand, one standard drink contains 10 grams of pure alcohol (ethanol). The standard-drink label on cans and bottles in NZ is based on this 10g definition. As a rough guide, one standard drink is:

A low-alcohol drink is defined in NZ as one containing 2.5% ethanol by volume or less. This matters for the host-responsibility duty to stock and promote low-alcohol options under the Sale and Supply of Alcohol Act 2012.

Blood Alcohol Concentration (BAC)

Blood Alcohol Concentration (BAC) is the weight of alcohol in a given volume of blood, expressed in New Zealand as milligrams of alcohol per 100 millilitres of blood (mg/100ml). It is a physiological measurement of how much alcohol is circulating in the bloodstream at a moment in time.

A Critical Exam Distinction

The NZ alcohol licensing regime does not define intoxication by a numerical BAC. Section 5 of the Sale and Supply of Alcohol Act 2012 defines intoxication as being observably affected by alcohol, other drugs, or other substances to a degree that shows two or more of:

• appearance affected
• behaviour impaired
• coordination impaired
• speech impaired

This is the SCAB tool you will apply in Chapter 8. A duty manager never needs a breath reading to refuse service — the observation of signs is sufficient and is the legally correct test.

Numerical limits you may have heard of come from the Land Transport Act 1998 drink-driving regime, and it is worth getting both the numbers and the units right because they are routinely garbled:

A reading in the band above the adult limit up to 400 micrograms per litre of breath (or 80mg per 100ml of blood) is dealt with as an infringement offence; above that band it becomes a criminal offence carrying fines, disqualification and, at higher levels or on repeat, imprisonment.

Note the units: 250 and 400 are microgram-per-litre-of-breath figures, not milligram-per-100ml-of-blood figures. Quoting "250mg/100ml" as a driving limit is five times the actual blood limit and is a giveaway error. More importantly, these are transport-law offences, not licensing-law tests — none of them tells a duty manager whether a patron is "intoxicated" under s5. The exam frequently tests whether you confuse the two regimes.

Effects by BAC Band (General)

The following bands are general physiological descriptions used in standard health-education texts (Te Whatu Ora, HPA). They are descriptive, not licensing-law thresholds:

Individuals vary widely; a chronic heavy drinker may show few visible signs at a BAC that would visibly affect a non-drinker. This is why observation of the individual, not a formula, is the legal test.

Age Effects

• Younger people typically have lower body mass, less developed tolerance, and less experience of their own limits. They can reach visible intoxication on fewer drinks and are also at higher risk of acute harm.
• Older people undergo changes that increase sensitivity: reduced liver enzyme activity, decreased total body water, slower metabolism, and a greater likelihood of medication interactions (covered in 5.4). An older patron may be visibly affected after one or two standard drinks.

Gender Effects

Females generally reach a higher BAC than males for the same amount of alcohol consumed. The physiological reasons are well established and should be presented as averages, not crude stereotypes:

1. Lower body water percentage — alcohol distributes in body water, and females typically have a lower proportion of water to total body weight, so the same dose is more concentrated.
2. Lower gastric alcohol dehydrogenase — the stomach lining contains ADH that begins metabolising alcohol before it reaches the bloodstream; females have lower gastric ADH activity, so more alcohol passes through unchanged.
3. Higher body fat percentage — fat holds less alcohol than water, so a higher fat-to-water ratio raises BAC for a given dose.

Fluctuations in hormone levels across the menstrual cycle can also affect sensitivity, though this is secondary to the three structural factors above.

Why It Matters for the Duty Manager

The exam expects you to explain that intoxication assessment is individual. The same drink count produces different BACs and different visible signs depending on age, sex, body composition, tolerance, food, rate of drinking and health. The duty manager assesses the person in front of them using observable signs, not the number of glasses on the table. This is also why host-responsibility training emphasises that staff should never assume 'they can handle it' based on a patron's usual drinking history.