Age of Drinking Onset and Unintentional Injury Involvement After Drinking

Context In 1997, unintentional injury was the leading cause of death for persons aged 1 to 34 years. Approximately one third of deaths due to unintentional injury in the United States are estimated to be alcohol related. Onset of drinking at an early age has been found to be associated with alcohol dependence, but whether early-onset drinking increases risk for unintentional injury while drinking is unknown.

Objective To explore whether persons who started drinking at an early age are more likely to have experienced unintentional injuries while under the influence of alcohol.

Design and Setting The National Longitudinal Alcohol Epidemiology Survey, a cross-sectional survey conducted in 1992 of a representative sample of the US population.

Participants A total of 42,862 randomly selected adults (response rate, 90%; mean age, 44 years).

Main Outcome Measures Unintentional injury involvement while under the influence of alcohol by age of drinking onset (categorized as <14 years, each age from 14-20 years, or ≥21 years).

Results Relative to respondents who began drinking at age 21 years or older, those who started before age 14 years as well as those who started at each intervening age up to 21 years were significantly more likely to have been injured while under the influence of alcohol, even after controlling for history of alcohol dependence, heavy drinking frequency during the period that they drank most, family history of alcoholism, and other characteristics associated with earlier onset of drinking. After adjusting for these variables, odds ratios for having been injured while under the influence of alcohol were as follows: for younger than 14 years, 2.98 (95% confidence interval [CI], 2.29-3.89); age 14 years, 2.96 (95% CI, 2.26-3.88); age 15 years, 3.14 (95% CI, 2.48-3.97); age 16 years, 2.38 (95% CI, 1.90-2.98); age 17 years, 2.12 (95% CI, 1.66-2.71); age 18 years, 1.33 (95% CI, 1.08-1.64); age 19 years, 1.42 (95% CI, 1.07-1.89); and age 20 years, 1.39 (95% CI, 1.01-1.91).

Conclusion Drinking onset at ages younger than 21 years is associated with having experienced alcohol-related injuries.

In 1997, 92,253 people died because of unintentional injuries, the leading cause of death in the United States for persons aged 1 to 34 years.¹ Of those deaths, 42,013 resulted from motor vehicle crashes,² and the balance from falls, drownings, burns, and unintended gunshot wounds.

Alcohol consumption increases the likelihood that persons will be injured while engaging in a variety of activities of daily living, including driving a motor vehicle, walking, swimming, and boating.^3-9 Nearly 40% of traffic deaths in the United States involve alcohol and at least 300,000 persons are injured annually in police-reported alcohol-related traffic crashes.¹⁰ Thirty-one percent of persons who died as a result of a nontraffic unintentional injury in 331 medical examiner studies in the United States from 1975 to 1995 had blood alcohol levels of 0.10 or higher.⁹

A recent analysis of the National Longitudinal Alcohol Epidemiology Survey (NLAES) found that age of drinking onset was strongly related to having experienced alcohol dependence during one's life as defined by the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria,¹¹ a finding previously reported in smaller studies and those using the Diagnostic Interview Schedule and the Diagnostic and Statistical Manual of Mental Disorders, Third Edition criteria.¹² Among both men and women with and without a family history of alcoholism, persons who began drinking regularly before age 14 years were at least 3 times more likely to experience diagnosable alcohol dependence during their life than those who did not drink until they were older than 21 years.

Alcoholism is the leading risk factor for injury.¹³ Alcoholism treatment,¹⁴ as well as programs that systematically screen injured persons for alcoholism and offer them brief intervention and referral to alcoholism treatment, can markedly reduce injuries.¹³ However, analyses of the NLAES survey also reveal that nearly one third of persons injured under the influence of alcohol never in their life met alcohol-dependence criteria. Early age of drinking onset may be an indicator of increased risk of alcohol-related injury even among persons who have not had diagnosable alcohol dependence. Questions in the NLAES survey permit us to explore whether early age of drinking onset was related to respondents drinking heavily, placing themselves in situations that increased their risk of injury, and having experienced an unintentional injury after drinking, even after controlling for alcohol dependence and other personal characteristics associated with the age respondents started drinking.

The NLAES is a national probability survey sponsored by the National Institute on Alcohol Abuse and Alcoholism. In 1992, the US Bureau of the Census administered face-to-face interviews with 42,862 noninstitutionalized respondents aged 18 years and older, mean age 44 years, residing in the 48 contiguous states and the District of Columbia.

The multistage sampling approach used for NLAES has been described in detail.¹⁵ Blacks and persons aged 18 to 29 years were oversampled, but the data were weighted in the analyses so that the sample is representative of the US population. The household response rate was 91.9% and the in-person response rate was 97.4%. The overall response rate was 90%.

Measures of alcohol use and dependence were derived from the Alcohol Use Disorder and Associated Disabilities Interview Schedule, a fully structured diagnostic psychiatric interview designed to be administered by trained interviewers who are not clinicians.

The Alcohol Use Disorder and Associated Disabilities Interview Schedule included a sequence of questions that measure alcohol dependence based on the criteria for alcohol dependence of the DSM-IV. Diagnosis of alcohol dependence required that in any 1 year a respondent must meet at least 3 of the following 7 criteria: (1) tolerance; (2) withdrawal or avoidance of withdrawal; (3) persistent desire or unsuccessful attempts to cut down or stop drinking; (4) spending a lot of time drinking, obtaining alcohol, or recovering from its effects; (5) giving up or reducing occupational, social, or recreational activities in favor of drinking; (6) impaired control over drinking; and (7) continuing to drink despite a physical or psychological problem caused or exacerbated by drinking. An independent test-retest study determined good reliability with a κ of 0.76 and a κ of 0.73 for past year and prior to past year dependence diagnoses, respectively.¹⁶

The age of drinking onset was ascertained by asking respondents who had consumed at least 12 drinks in any year of their life how old they were when they first started drinking, not counting small tastes or sips of alcohol. In an independent test-retest study before the full NLAES was conducted, the test-retest reliability of the drinking onset variable was good with a κ of 0.72.¹⁶

In this study, a respondent was classified as family history positive if any of their first-degree relatives (ie, parents, siblings, children) were reported as having been alcohol dependent or abusers consistent with DSM-IV criteria. In a test-retest study, the family history items showed good-to-excellent reliability with a κ at 0.72 for fathers, 1.00 for mothers, 0.90 for brothers, 0.73 for sisters, and 0.65 each for sons and daughters.¹⁶

Current heavy drinking was determined by asking respondents: "During the past 12 months, about how often did you have five or more drinks of any type of alcohol in a single day?" Respondents were also asked: "About how often would you say you usually drank enough to feel drunk during the last 12 months? By drunk, I mean times when your speech was slurred, you felt unsteady on your feet or you had blurred vision." We also constructed a measure of the frequency with which respondents drank 5 or more drinks during their period of heaviest drinking in their life. Respondents were asked whether there were periods in their life when they drank more than in the past year. Respondents who answered yes were then asked their frequency of drinking and the amounts they usually consumed on days they drank during this period. They were also asked what was the greatest amount they drank on any day during that period and how frequently they drank that amount. We used data from these questions as well as questions about frequency of drinking 5 or more drinks in the past year to determine their frequency of drinking 5 or more drinks during their period of heaviest drinking.

Taking risks that might lead to injury was assessed by the following questions, "In your life, did you ever get into a situation while drinking or after drinking that increased your chances of getting hurt—like swimming, using machinery, or walking in a dangerous area or around heavy traffic? Did that happen in the past 12 months?" Lifetime and past year alcohol-related injury involvement were explored by asking respondents: "In your entire life, did you ever accidentally injure yourself under the influence of alcohol, for example have a bad fall, or cut yourself badly, get hurt in a traffic accident, or anything like that? Did this happen in the past 12 months?"

All statistical analyses were conducted using the SUDAAN statistical package to account for the survey design.¹⁷ Age of drinking onset was categorized as younger than 14 years, each year separately from 14 through 20 years, and 21 years or older (the minimum legal drinking age throughout the United States). Analyses focused only on respondents who currently drink and formerly drank and who responded to this question. The significance of relationships between age of drinking onset and respondent background characteristics was tested using χ² analysis.

We examined the relationship between age of drinking onset and frequency of heavy drinking, adjusting for background characteristics including history of alcohol dependence through a series of multiple logistic regression analyses. We examined the following outcomes as dichotomous variables: whether respondents drank at least 5 or more drinks at least once per week in the past year; drank to intoxication at least weekly in the past year; or drank 5 or more drinks at least daily during the period when respondents drank most heavily. Odds ratios and 95% confidence intervals were calculated describing the increased risk of these outcomes for those with drinking onset before age 14 years and at each age from 14 through 20 years relative to those who started drinking at or after age 21 years.

To assess whether age of drinking onset was related to injury outcomes, we also conducted multiple logistic regression analyses examining, as dichotomous outcome variables, whether respondents ever or in the past year got into a situation while or after drinking that increased their risk of injury; or unintentionally injured themselves while under the influence of alcohol.

The regression analyses were conducted twice. First, we entered the personal, social, and demographic characteristics associated with age of drinking onset, excluding alcohol dependence and measures of heavy drinking frequency, then we added measures of alcohol dependence and heavy drinking. This was done to assess whether any relationships between age of drinking onset and injury involvement were primarily a function of those who started drinking earlier in life being more likely to experience more frequent heavy drinking episodes.

We entered the frequency of heavy drinking during the respondent's heaviest drinking period into the regression analyses examining lifetime exposure to injury risk and involvement, and the past year frequency of heavy drinking measures into the regression analyses examining past year exposure to injury risk and injury involvement. For consistency across models, the entire set of background variables was included in the analysis of each drinking and injury outcome.

Respondent characteristics are listed in Table 1. Several subgroups in the study were significantly more likely to have begun drinking at earlier ages: respondents who were male, younger, never married, who had less than a high school education, who currently or ever smoked or used illicit drugs, or who were currently or ever dependent on alcohol, and respondents reporting a family history of alcoholism (all relationships, P<.001; data available on request).

Frequent heavy drinking in the past year and during the period when respondents drank most was associated with greater risk of injury involving alcohol. To illustrate, 29% of respondents who drank to intoxication at least weekly in the past year were in a situation that year after drinking that increased their risk for injury compared with 3% of drinkers who never drank to intoxication in the past year (P<.001). Seventeen percent who drank to intoxication at least once per week in the past year were injured under the influence of alcohol in the past year compared with 0.1% of drinkers who never drank to intoxication in the past year (P<.001).

Respondents who began drinking at younger ages were much more likely than those who did not start drinking until they were 21 years or older to report heavy drinking both in the year prior to the survey and during their period of heaviest drinking (Figure 1). Those who started drinking prior to age 14 years were more than 3 times likely to report consuming 5 or more drinks on a single day at least once per week during the past year. They were 7 times more likely to report drinking enough to be intoxicated at least once per week. Further, they were 3 times more likely to report drinking 5 or more drinks at least once per week during their period of heaviest drinking.

The regression analyses examining the relationship between age of drinking onset and drinking behavior revealed that even after controlling for diagnosis of alcohol dependence and other variables related to age of drinking onset, the younger respondents were when they started drinking, the more likely they were in the past year to drink 5 or more drinks on an occasion and to drink to intoxication at least once per week (Table 2). Compared with those who began drinking at age 21 years or older, those who began before age 14 years were nearly 1.4 times more likely to drink 5 or more drinks and 2.8 times more likely to drink to intoxication at least weekly in the past year. They were also 2.8 times more likely to consume 5 or more drinks daily during their period of heaviest drinking during their lifetime.

Early age of drinking onset was also strongly related to both being in situations while or after drinking that increased a person's chances of being injured and being injured while under the influence of alcohol. Compared with respondents who began drinking at age 21 years or older, those who began drinking prior to age 14 years were nearly 7 times more likely to report having been in situations that increased their chance of injury ever in their lifetime and in the past year (Figure 2). Persons drinking prior to age 14 years were also 12 times more likely to have ever been injured while under the influence of alcohol ever in their lifetime and in the past year (Figure 3). These relationships were generally monotonic from drinking age onset at age 14 years to age 21 years or older. The younger respondents were when they began drinking, the more likely they were to have been in situations that increased injury risk and to have been injured under the influence of alcohol.

The regression analyses on injury outcomes (not including alcohol dependence and drinking measures) (Models 1A and 1B in Table 3 and Table 4) revealed that even after controlling for other personal characteristics associated with age of drinking onset, respondents who began drinking before age 14 years relative to those who started at age 21 years or older were 4.8 times more likely to have ever been in a situation after drinking that increased their risk of injury and 2.4 times more likely to have done so in the past year. They were also 4.9 times more likely to have ever been injured while under the influence of alcohol and 3.2 times more likely to have been injured this way in the past year. Even when we also included in the regression analysis measures of alcohol dependence, frequency of drinking 5 or more drinks during a respondent's period of heaviest drinking, and past year frequency of drinking 5 or more drinks or to intoxication (Models 2A and 2B in Table 3 and Table 4), each of which were independently related to our study outcomes, those who began drinking prior to age 14 years relative to those who started at 21 years or older were 3 times more likely ever and 1.5 times more likely in the past year to have been in a situation after drinking that increased their risk of injury. They were also 3 times more likely ever and 2 times more likely in the past year to have been injured while under the influence of alcohol.

Further, lifetime elevated injury risks were not confined to those who began drinking before age 14 years. Persons who began drinking in each age group younger than 21 years relative to those who started when they were 21 years or older were significantly more likely during their lives to have ever been injured while under the influence of alcohol and to have placed themselves in situations after drinking that increased their risk of injury. This was found even after controlling for history of alcohol dependence, frequency of heavy drinking during respondents' heaviest drinking period, and numerous other characteristics related to age of drinking onset (Model 2A in Table 3 and Table 4).

Our analyses indicate that a large part, but not all, of the relationship between early age of drinking onset and unintentional injury while under the influence of alcohol in the past year resulted from those who began drinking at an early age reporting more frequent heavy drinking in the past year. Persons who began drinking in each age group 17 years and younger were significantly more likely than those starting at age 21 years and older to have been injured after drinking in the past year when we controlled for the initial set of characteristics related to age of drinking onset (Model 1B in Table 4). However, after further adjusting for diagnosis of alcohol dependence and for frequency of drinking 5 or more drinks on an occasion or to intoxication in the past year, only those who began drinking prior to age 14 years were still significantly (2 times) more likely to have been injured in the past year while under the influence of alcohol (Model 2B in Table 4).

Frequent heavy drinking in the past year, which is more common among those who started drinking early in life, is particularly problematic given the disproportionate willingness of people who began drinking early in life to place themselves in situations after drinking that increase their risk of injury (Table 3). Even after controlling for measures of current alcohol dependence and past year frequency of drinking 5 or more drinks or to intoxication, persons who began drinking prior to age 18 years were also significantly more likely than those starting at age 21 years or older to place themselves in situations after drinking in the past year that increased their risk of injury (Model 2B in Table 3).

Strategies to delay the age persons begin drinking, such as the minimum legal drinking age of 21 years, have been found to reduce drinking,¹⁸ alcohol-related traffic deaths,¹⁹ and deaths from other unintentional injuries among persons younger than 21 years.²⁰ One study indicated that the law also reduced drinking among persons 21 to 25 years who grew up in states with minimum legal drinking ages of 21 years relative to other states,¹⁸ but the effect of the law on injury involvement during adult years was not studied. Previous US studies have also indicated that the younger people are when they begin drinking, the greater the likelihood they will experience alcohol dependence during their lifetime.^11,12

This report indicates that early age of drinking onset is associated with frequent heavy drinking later in life not only for persons with diagnosable alcohol dependence, but other drinkers as well. This, in turn, heightens the risk of alcohol-related injuries for persons both when they are below and above the legal drinking age of 21 years. Further, those who began drinking at younger ages more often report placing themselves in situations after drinking that increase risk of injury, not only when they are younger than 21 years, but also as adults. This was found not only among respondents dependent on alcohol and others who frequently drink heavily and to intoxication, but also among other respondents who drink. Finally, persons who began drinking in each age group younger than 21 years relative to those starting after age 21 years were significantly more likely during their lives to have been injured while under the influence of alcohol. This was found even after controlling for history of alcohol dependence, frequency of heavy drinking during respondents' heaviest drinking period, and numerous characteristics related to age of drinking onset.

We should caution that this study's results were based on self-report in a cross-sectional survey, and hence may be subject to limitations associated with self-report. On the one hand, social desirability biases may foster underreporting of alcohol use and injury involvement after drinking. On the other hand, persons willing to report heavy drinking may be less hesitant than others to report injury involvement after drinking. Although the sample was nationally representative, large, and the response rate was excellent, it would be useful to replicate these results in a longitudinal study with chemical markers in addition to self-report.

It is possible that people who engage in a variety of deviant or illegal behaviors at an early age are more likely to continue them later in life. For example, childhood conduct disorder has been associated with substance abuse later in life.²¹ However, the relationships between early drinking onset and recent heavy drinking and injury involvement were independent of the current or past use of illegal drugs or tobacco.

Our findings indicate a need for additional research in 2 areas. First, research is needed to explain why starting to drink at an early age relates to alcohol dependence and to heavier drinking later in life, even among persons who are not dependent. Genetics may play a role by predisposing certain individuals to exhibit tolerance to the physiologic effects of alcohol early in their drinking careers, thereby contributing to the establishment of heavier drinking patterns that persist later in life.²² Familial influences, both genetic and environmental, may account for the early onset/later dependence relationship.²³ Persons who drink earlier may have physiologic changes that contribute to greater tolerance and the need to drink more to achieve the same pleasurable sensations after drinking. Persons who started drinking earlier in life may have learned to drink in less controlled situations with peers whose drinking norms are to drink to intoxication rather than with family and parents who might drink more moderately. Also, persons who develop alcoholism later in life may have had more adverse experiences in childhood such as psychological, physical and sexual abuse, domestic violence, and substance abuse by parents.²⁴ Drinking earlier and more heavily may be an attempt to cope with these experiences.

Second, research needs to examine why, even when diagnosis of alcohol dependence and measures of frequency of lifetime and past year heavy drinking are controlled, persons who began drinking at an earlier age are more likely after drinking to place themselves in situations that pose risk of injury. Several explanations are possible. Those who begin drinking at an early age may be less fearful of injury and situations that pose risk of injury. Some may derive pleasure or a sense of self-esteem by taking risks associated with injury. It is well-known that persons who drive after drinking, for example, are more likely to speed and are less likely to wear seat belts.²⁵ Alternatively, persons who start drinking at earlier ages may not be as aware or appreciate how alcohol increases injury risk. Studies have shown that people who drive after heavy drinking are more likely to believe they can drive safely after higher amounts of alcohol consumption.²⁶ They may believe for example the risk of traffic crashes and other injuries increase only for people who are visibly intoxicated. Also, their heavier consumption of alcohol may further impair the judgment of those who start drinking at a younger age. After drinking, they may be less likely than when sober to recognize situations that pose risk of injury or to fully appreciate the risks posed by those situations.

While research needs to be done to determine whether delaying the onset of drinking will prevent alcohol-related injury later in life, we think our findings provide important information for physicians and other health care providers to share with their adolescent patients about risks associated with early age of drinking onset. They should explore the age their patients started to drink and advise their patients that people who start drinking at early ages not only have an increased risk of developing alcohol dependence, they also have an increased risk of experiencing motor vehicle and other unintentional injuries, which are the major causes of death among adolescents and young adults. Recent national surveys indicate that after a decade of decline, the percentage of high school seniors who drink, drink heavily, and drive after drinking has increased in the past 2 years.²⁷ The study reported here supports efforts to expand clinical, educational, legal, and community interventions that delay onset of drinking.