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Do Circumstances in Early Life Contribute to Tooth Retention in Middle Age?

¹ Paediatric and Lifecourse Epidemiology Research Group, School of Clinical Medical Sciences, Sir James Spence Institute, Royal Victoria Infirmary, University of Newcastle upon Tyne, Newcastle upon Tyne NE1 4LP, UK; and
² School of Dental Sciences, University of Newcastle upon Tyne, UK;

^* corresponding author, M.S.Pearce{at}ncl.ac.uk

	ABSTRACT

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The relative contributions of factors operating in fetal life, childhood, and adulthood to risk of disease in middle age have become an important research issue, though oral health has rarely been considered. This study investigated the relative impacts of risk factors operating at different stages throughout life on the number of teeth retained at ages 49–51 yrs based on data from the Newcastle Thousand Families cohort. Very little variation in tooth retention in middle age was explained by factors operating at earlier stages in life. The previously noted relationship between childhood socio-economic status and oral health in adulthood appears, with respect to tooth retention, to diminish with increasing age as adult socio-economic position and lifestyle factors have an increasing effect. Promotion of a healthier adult lifestyle and continued improvements in oral hygiene would appear to be the public health interventions most likely to increase tooth retention in middle age.

KEY WORDS: cohort • epidemiology • oral health • socio-economic status • teeth

	INTRODUCTION

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It has been proposed that the risk of adverse health (such as diabetes, cardiovascular disease, and osteoporosis) in middle age may be ‘programmed’ by impaired development in utero (Barker, 2003). However, experiences in infancy, childhood, and adulthood may also determine adult health, independently of fetal life (Gliksman et al., 1995; Davey Smith et al., 1998). The risk of poor oral health in adulthood has been linked to socio-economic status in childhood (Poulton et al., 2002), but there are also many studies linking conditions in adulthood to oral disease and tooth loss. When assessing the effects of factors operating at different stages of an individual’s life on his/her risk of adult disease, one should use information from across the whole lifecourse (Kuh and Ben Shlomo, 1997). Such investigations assessing which stages of life are of most importance to an individual’s health have rarely included oral health, but may give an overall context for assessing oral disease risks and planning prevention that cannot be achieved by other methodologies.

The Newcastle Thousand Families cohort, consisting of all 1142 children born in May and June, 1947, to mothers resident within the city of Newcastle upon Tyne, provides an opportunity to apply a lifecourse approach to oral health. Two-thirds of these children were followed up until the age of 15 yrs (in 1962), with detailed information collected on their health, growth, and socio-economic circumstances (Lamont et al., 1998). We used these early life data, together with more recent data on adult health and lifestyle for the same subjects, collected at age 50 yrs, to quantify the direct and indirect effects of characteristics of fetal life, infancy, childhood, and adulthood on tooth retention at ages 49–51 yrs. The aim of the study was to establish the relative impacts of the risk factors operating at different stages throughout the lifecourse.

	MATERIALS & METHODS

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Participants in this investigation were cohort members who either contacted the study team in response to media publicity or were traced through the United Kingdom National Health Service Central Register. Between October, 1996, and December, 1998, self-completion questionnaires on health and lifestyle were sent out, and study members were invited to attend for clinical examination and to take part in further studies (Kanan et al., 2000; Lamont et al., 2000; Wright et al., 2001; Parker et al., 2003; Wright and Parker, 2004). The presence of each tooth was recorded by one of two specifically trained research nurses as part of the clinical examination. Ethical approval for the study was obtained from Local Research Ethics Committees, and all participating study members gave their written informed consent.

Explanatory variables were grouped within a conceptual framework (Victora et al., 1997) according to the lifecourse stage at which they would be expected to operate on the risk of future poor oral health (Fig.). This approach allows the individual effects of variables on tooth retention to be examined, while also giving the opportunity for an overall effect of factors operating at a similar stage in an individual’s life to be investigated.

View larger version (19K): [in this window] [in a new window]   Figure. Conceptual framework for fetal, infant, childhood, and adult influences on tooth retention at age 49–51 yrs. The solid lines represent the direct effects of each stage of the lifecourse on the number of retained teeth. The dashed lines represent indirect effects mediated through later stages of the lifecourse.

Data on adult health and lifestyle were collected by self-completion questionnaire at age 49–51 yrs (Lamont et al., 2000). Occupational details of the main wage-earner in the household at age 50 were coded according to the 1990 UK Registrar General’s Standard Occupational Classification, and hence the social classes were derived (OPCS, 1990).

Four categories of alcohol consumption at age 50 were derived (Power et al., 1998). Light drinking was defined as up to 5 units of alcohol per wk for women (10 units for men) and moderate drinking as up to 21 units for women and 28 units for men. The number of pack-years of cigarettes smoked (i.e., one pack-year equals one pack of cigarettes smoked per day for one yr) was estimated from the study members’ smoking habits at ages 15, 25, 35, and 50 yrs as recorded on the self-completion questionnaire at age 50. Cross-sectional data, at age 50, on total dietary sugars consumed per day were estimated from the European prospective investigation of causes and nutrition (EPIC) food frequency questionnaire (Bingham et al., 1997). Hormone replacement therapy (HRT) used was derived from the questionnaire at age 50 and defined as ‘ever having had HRT’ or ‘never having had HRT’.

Statistical Analysis
Twins were excluded from all analyses. Separate analyses were carried out for men and women, since lifecourse effects on adult health have previously been suggested to differ by gender for this cohort (Lamont et al., 2000; Parker et al., 2003). The relationships between the total number of teeth and explanatory variables were estimated by multiple linear regression. Study members with missing data were included in all analyses for which they contributed complete data. The percentage of total variance in the number of retained teeth directly accounted for by each lifecourse stage was estimated by the difference in R² between regression models with and those without the variables in the lifecourse stage of interest, and including all other variables in the regression model. The overall effect of early life, including indirect effects mediated through factors operating in adulthood, was estimated by the value of R² from a regression model containing those variables operating in early life alone. We estimated corresponding confidence intervals by ‘bootstrapping’ the R² statistic on 10,000 repeated samples of the same size, drawn with replacement from each dataset (Stine, 1990).

The statistical software package Stata, version 8.0, was used for all analyses (STATA, Release 8.0, StataCorp, College Station, TX, USA).

	RESULTS

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Of the original 1142 study members from 1947, 832 were traced at age 50 yrs (Lamont et al., 2000), 574 completed the health and lifestyle questionnaire, and, of the 412 study members who attended the health check, 337 (141 men, 196 women) underwent the clinical dental examination. This sample did not differ significantly (p > 0.05) from the members of the original cohort not included in this analysis in terms of any of the factors acting at birth, infancy, and childhood, with the exception of gender (p < 0.001). The number of teeth retained by men and women did not differ significantly (median = 25 and 24, respectively; p = 0.28). Nine male and nine female study members were edentate; only one male and two females had retained all their teeth to the age of 50 yrs. Descriptive statistics for all explanatory variables are given in Tables 1 and 2.

Relative Contribution of Each Stage in the Lifecourse
The explanatory variables included in this study accounted for 25% of the total variation in the number of teeth retained at age 50 in men, and 35% of the variation in women. Birth weight and socio-economic and housing position at birth accounted for less than 2% of the total variance in the number of teeth retained at age 49–51 in both men and women (Table 3). The direct effects of infant and childhood experience contributed 1.5% of the variance in men and 3.0% of that in women. The overall contribution of all early life variables, including indirect effects mediated through adult lifestyle and socio-economic position, was 8.1% for men and 12.9% for women. Adult socio-economic position and lifestyle accounted directly for 17.2% of the total variance in men and 21.9% of that in women. The majority of all explained variation in the number of teeth retained at age 49–51 in both men and women was contributed exclusively by adult factors.

	DISCUSSION

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Of 1142 men and women recruited at birth in 1947, 337 participated in the study. Our inclusion rate of 30% of the original cohort is greater than that reported in several similar studies investigating the effects of early life factors on health later in life (Parker et al., 2003). Longitudinal studies of this nature allow for comparison of the characteristics of the initial and final samples and the identification and management of any major biases, should they be present. The study members participating in this study did not differ significantly from the remainder of the original cohort with respect to any factor in early life other than gender, by which separate analyses were undertaken. In addition, inclusion of cohort members who had moved out of the study region (18% of those who participated in the health check were resident outside the Northern Region) increased the representativeness of the population studied. Furthermore, the clinical dental status of those included in this study did not differ significantly from that of a national sample aged 45–54 yrs who participated in the 1998 UK Adult Dental Health Survey (Kelly et al., 2000). We can be confident that the participants examined were representative of the whole cohort.

Those women from the more advantaged social classes in adulthood tended to have more retained teeth than less-advantaged women, consistent with previous findings on a similar cohort in the UK (Kelly et al., 2000). A study of 1000 adults from New Zealand at age 26 yrs showed significantly poorer oral health among those study members with low socio-economic status in childhood compared with those from the highest socio-economic group (Poulton et al., 2002). This effect was independent of adult socio-economic status, although the effect of adult socio-economic status is likely to increase with age, since the related risks to oral health are cumulative. While the univariate analysis of the data for the women in this study confirmed the finding of a relationship between childhood socio-economic status and an aspect of oral health, the effect was not independent of adult socio-economic status at the later age of 49–51 yrs. It is possible that this may reflect the upward social mobility (from occupational social class of the main wage-earner of the household in childhood, usually the father, to that of the household in adulthood) seen in this particular cohort. Similar effects may not be seen in cohorts born in later times or in different geographical areas when social mobility is not so widespread.

In both men and women, only individual factors acting during adulthood were independently significant in the prediction of number of teeth at age 50 yrs. A high number of cigarette pack-years smoked was associated with a decreased number of teeth remaining in both genders, consistent with previous findings (Tonetti, 1998; Albandar et al., 2000; Machuca et al., 2000). Smoking itself may be a causal factor for tooth loss, through its influence on the severity of both periodontal disease and caries; however, it may also act as a surrogate for a range of behavioral and lifestyle factors not available to this investigation, such as dental attendance and oral hygiene behaviors over the whole lifecourse.

In women, those who never drank alcohol tended to have fewer teeth than those who did, perhaps surprisingly including those classed as ‘heavy drinkers’. While most previous research linking increased alcohol consumption with poor oral health has considered the effects of only alcoholism, it has been suggested that moderate alcohol consumption may be a risk factor for periodontal disease, independently of oral hygiene (Tezal et al., 2001). However, a J-shaped relationship between alcohol consumption and some indicators of poor oral health was also observed (Tezal et al., 2001). The cross-sectional data collected in the current study may be prone to reporting bias, and the group of non-drinkers may include individuals who no longer drink due to medical reasons.

The dietary data available for the analysis were relatively crude and available only for subjects at age 50. The measure of sugar intake used was based on estimated total sugar intake, and the contribution of sugars to the overall model is likely to be an underestimate. More detailed information, from childhood as well as adulthood, based on frequency and types of sugar intake would be expected to increase further the explained variation in the number of teeth retained at age 50.

In both men and women, factors acting during adult life accounted for the majority of the explained proportion of variation in the number of teeth at age 50 yrs. Relatively little of the explained variation in oral health in middle age was accounted for by factors operating at earlier stages in life. Little has been published regarding lifecourse determinants of tooth retention in middle age. However, the finding that adult lifestyle was the most important determinant of tooth retention was consistent with reports from other studies where data from the Thousand Families cohort were used to explore adult health and disease. To date, analysis of the data from the cohort has demonstrated that adult lifestyle and biological risk markers appear to play the most important role in predicting cardiovascular disease (Lamont et al., 1998) and hyperinsulinemia, dyslipidemia, and obesity (Parker et al., 2003).

The promotion of a healthier adult lifestyle and continued improvements in oral hygiene throughout the whole lifecourse would appear to be the public health interventions most likely to increase tooth retention in middle age.

	ACKNOWLEDGMENTS

 
This work formed part of the BMedSci degree completed by JM and was funded through a bursary from PPP Healthcare. We thank all the Thousand Family Study members for taking part in this study and the study teams past and present. We thank the Wellcome Trust, the Minnie Henderson Trust, the Sir John Knott Trust, and the Special Trustees of the Newcastle Hospitals for funding. Jan Gebbie and Jean Gerrard carried out the oral health examinations. EPIC food frequency questionnaires were analyzed by the MRC Dunn Clinical Nutrition Centre, Cambridge.

Received November 21, 2003; Last revision March 26, 2004; Accepted April 29, 2004

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