1 Skin Cancer Research Group, North Queensland Center for Cancer Research, School of Public Health and Tropical Medicine, James Cook University, Townsville, Queensland, Australia
2 Queensland Institute of Medical Research, Brisbane, Queensland, Australia
Correspondence to Dr. Simone L. Harrison, Skin Cancer Research Group, School of Public Health and Tropical Medicine, James Cook University, Townsville, Queensland, Australia 4811 (e-mail: simone.harrison{at}jcu.edu.au).
Received for publication June 22, 2004. Accepted for publication November 4, 2004.
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ABSTRACT |
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child; clothing; health behavior; intervention studies; nevus; skin neoplasms; sunlight
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INTRODUCTION |
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The most important biomarker for melanoma is an increased number of melanocytic nevi (moles) (2), and children raised in Queensland develop common (8
11
) and atypical (12
) melanocytic nevi earlier and in higher numbers than children elsewhere. Melanocytic nevi are precursor lesions of a substantial proportion (up to 60 percent) of melanomas (13
). Because sun exposure is related to nevus development during childhood (8
11
, 14
), melanocytic nevi offer a short-term measure of the efficacy of sun-protection interventions.
Few childhood sun-protection intervention studies have been reported. Most of the studies educated children and/or their caregivers about sun protection (1518
) or provided high-sun-protection-factor sunscreens (19
, 20
). To date, we know of only one study that has reported a statistically significant reduction in the development of melanocytic nevi (19
).
In this paper, we present the design and baseline results of a sun-protection intervention in child-care centers in Townsville, Australia. The study commenced in 1999 and appears to be the first controlled intervention trial aimed at reducing sun exposure and, hence, the incidence of melanocytic nevi in young children primarily through regular use of sun-protective clothing.
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MATERIALS AND METHODS |
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Recruitment
In June 1999, all 26 of the local day-care centers that provided care for infants and children 5 full days a week were invited to participate. Twenty-five (96.2 percent) agreed.
Prior to commencing the study, the availability and quality of shade at each facility was assessed by measuring the ratio of covered to uncovered play areas and the vertical and horizontal penetration of sunlight for at least five shade structures. Results were given to center directors during recruitment.
During random assignment of centers into intervention (n = 13) and control (n = 12) groups, each intervention center was matched with a control center on the basis of shade provision (three levels) and the socioeconomic status of the suburb by using the SEIFA index (three levels) (23). Permission to obtain enrollment lists comprising the first name, date of birth, and attendance pattern of children less than age 3 years was obtained from center directors. A study information sheet, a questionnaire, and a consent form were sent to the parents of eligible children via the child-care centers.
Participants
The study included all Caucasian (at least two grandparents of European origin) children aged 035 months who regularly attended a participating child-care center between November 1999 and July 2002, and whose parents intended to remain in Townsville and gave their written informed consent to participate (n = 652).
Clinical examination
At baseline, the first author (S. L. H.) performed full-body examinations (30 body sites excluding the buttocks, genitals, and scalp) for melanocytic nevi of all sizes on all children based on a standard international protocol to define and count melanocytic nevi (24). These examinations are repeated annually for 3 years (to be completed in July 2005).
It was not possible to blind the examiner to the random assignment because of close involvement in the study. However, very high concordance of melanocytic nevus counts was found for 49 children in March 2003 between the study examiner and an experienced visiting dermatologist (14) (concordance correlation coefficient = 0.97, 95 percent confidence interval: 0.95, 0.98) (25
).
Height, weight, and hair and eye color were recorded. Skin reflectance of the inner upper arm was determined with a reflectance spectrophotometer (Evans Electroselenium Ltd., model 99; Diffusion Systems Ltd., London, United Kingdom) at 685 nm for melanin discrimination (high skin reflectance correlates with fair skin) and then categorized as fair/medium/olive on the basis of previously used cutpoints (26). Baseline measurements were missing for 56 children because of instrument repairs. Subjective skin color was assigned to these children (53 fair, three medium).
Questionnaire
All parents completed a comprehensive baseline questionnaire covering the children's demographic and pigmentary characteristics, sunburn history, sun exposure, and sun-protection habits. Habitual sun exposure at baseline was assessed by using charts. Parents marked the amount of time that their child usually spent outside in the sun on a line from 6 a.m. to 7 p.m. Information about the hours spent outside on typical weekdays and weekends and the frequency of "playing outside in the sun during the warmer months of the year" was collected. "Total hours spent outside during the warmer months" and "total hours spent playing in water during the warmer months" were estimated from this information.
Sunburn history was assessed with three questions about the frequency of sunburns resulting in "redness without peeling," "redness with peeling," and "pain and blistering." The frequency of each type was weighted 1, 2, and 3, respectively, and was summed to give a combined severity score. Parents were asked to mark, on a body-site diagram, those areas that had been sunburnt. A score for the extent of sunburn was obtained by summing the respective body sites and adjusting according to the surface area affected (2731
). Another combined score of the extent and severity of sunburn was created by multiplying the two scores. Similarly, parents marked the body sites on which "sunscreen was usually applied on a typical day." A score for sunscreen protection was created by summing the number of body sites adjusted for surface area (27
31
) and multiplying by frequency of use at home during 1) summer and 2) winter (never = 0, less than half the time = 1, half the time = 2, more than half the time = 3, almost always = 4).
Scores for hat and swimwear protection were derived from questions about type and frequency of use during 1) summer and 2) winter. A score for hat use was created by multiplying the responses for the following variable: "What does your child wear on his or her head most often when outdoors?" (nothing = 0, a cap = 1, a wide-brimmed hat = 2, a legionnaire hat = 3) and the sum of the responses to these questions: "How often does your child wear this hat when he or she is outdoors during 1) summer and 2) winter?" (never = 0, less than half the time = 1, half the time = 2, more than half the time = 3, almost always = 4). Likewise, a score was created for swimwear protection by multiplying responses for these variables: "What does your child wear most often when he or she is playing in water?" (nothing = 0, shorts/briefs = 1, two-piece swimsuit = 2, one-piece swimsuit = 3, shorts/one-piece/briefs and a T-shirt = 4, Lycra (nylon elastane; E. I. du Pont Nemours & Co., Inc., Wilmington, Delaware) cover-up suit = 5) and "How often does your child wear this when he or she is playing in water?" (never = 0, less than half the time = 1, half the time = 2, more than half the time = 3, almost always = 4) for summer and winter.
Intervention design
Each of the 13 child-care centers in the intervention group was given enough legionnaire hats and high UPF T-shirts and shorts to clothe all children in their baby and toddler units (which care for children less than age 3 years). Intervention child-care staff members were trained to dress the children in this clothing on arrival each day to ensure that the trunk, posterior neck, upper arms, and thighs were covered when outdoors. Laminated signs on the exit doors of intervention child-care buildings reminded staff to dress all children in the sun-protective clothing before going outdoors. Dirty garments were collected twice a week from intervention centers by research staff, the garments were laundered, and compliance with the intervention was observed (table 1). Weekly laundry volumes were monitored. The parents of children in the intervention group were educated about the appropriate use of protective clothing at the center and at home, and they were given legionnaire hats for home use and garments made of fabrics in the "excellent" ultraviolet radiation protection category to wear during water activities.
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Clothing design
Advice about suitable fabrics was sought from local clothing manufacturers, their suppliers, and Dr. Peter Gies from the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). Samples of fabrics with properties usually associated with low ultraviolet radiation transmission (tight weave, darker colors, etc.) (32) were discussed with the staff of the intervention child-care centers. Samples of cotton and nylon taslon (a fine, lightweight, shower-proof fabric) in a range of colors were sent to ARPANSA for UPF testing, and the fabrics with the highest mean UPF measurements were chosen.
Prototype T-shirts, shorts, and long-sleeved shirts in sizes 08 were tested on 200 infants and preschool children to ensure that they would adequately cover the trunk, thighs, and upper arms. The T-shirts were made from 100 percent cotton in five colors (sizes were color coded for staff convenience) with UPF ratings in the "very good" protection category (a UPF range of 2539 blocks 9697.4 percent of ultraviolet radiation) (21). The standard sleeve length for each size was extended by 21 percent to ensure that the sleeves were at least elbow length. The shorts covered the legs to below the knees and were made from water-resistant nylon taslon in five colors, with UPF ratings in the "excellent" protection category (a UPF range of 4049, 50+ blocks
97.5 percent of ultraviolet radiation) (21
). The long-sleeved shirts were made of the same fabric, with contrasting colored cuffs and neckband. To prevent contamination of the control population, these garments were manufactured for the study only.
Outcome measures
Total number of melanocytic nevi was the main target variable for the present baseline assessment. For a more convenient description of main risk factors, melanocytic nevi were dichotomized by using the median (1 vs. >1) as the cutpoint, thus enabling multivariate logistic regression analysis to produce effect measures (e.g., prevalence odds ratios) rather than regression coefficients.
Power calculations
Estimation of the required sample size was initially based on achieving a 24 percent reduction in the total number of melanocytic nevi (all sizes) and a 30 percent reduction in melanocytic nevi 2 mm by 4 years of age, a choice based on reducing the prevalence of melanocytic nevi at age 4 years to that expected for children of that age raised in Sydney, which has less ambient ultraviolet radiation (8
). To achieve a power of 80 percent and a significance level of 0.05, two groups of 72 children (standard deviation (SD), 26) were required to detect a 24 percent reduction in mean total number of melanocytic nevi (Townsville = 52.3, Sydney = 40), and two groups of 110 (SD, 10) were required to detect a 30 percent reduction in melanocytic nevi
2 mm (Townsville = 12.7, Sydney = 8.9) by age 4 years (8
, 9
). Thus, the study was planned to prevent an average of 12.3 incident melanocytic nevi (all sizes) and of 3.8 incident melanocytic nevi
2 mm (medians = 12 and 3, respectively) over a 3-year period. A third body-site-specific hypothesis was formulated based on preventing a mean of 3.8 melanocytic nevi (25 percent reduction; median = 3.75, SD, 10.0) on the arms in 3 years (sample size: 110 children/group assuming the same specifications as for the two other hypotheses).
Sample size calculation (adjusted for multiple testing of the three main hypotheses, violation of normality assumptions, and the design effect (1.5) of cluster sampling) estimated a necessary sample size of 230 children per group. Because the Townsville population is transient, the sample size was increased to account for loss to follow-up during the 3-year study period.
Statistical analysis
All numerical variables with a skewed distribution were described by using median values and interquartile ranges (IQRs); approximately normally distributed numerical variables were described by using means and standard deviations. The density of melanocytic nevi was calculated by using the formula suggested by the US Environmental Protection Agency (27).
Bivariate analysis of risk factors for melanocytic nevi initially used standard statistical tests (chi-square test, t test, nonparametric Wilcoxon test, Pearson and Spearman correlation coefficients). Bivariate results of parametric tests and chi-square statistics were adjusted for the cluster sampling design by using the survey commands in Stata statistical software, release 8.0 (Stata Corporation, College Station, Texas). Adjustment of nonparametric test results for the cluster sampling design was not directly possible. Therefore, numerical characteristics with skewed distributions were log-transformed to enable comparisons of adjusted transformed mean values. For those characteristics, the untransformed median values and IQR were presented together with the adjusted and unadjusted p values. The success of the randomization process was assessed bivariately by comparing children in the intervention group with children in the control group regarding all potential risk factors considered. These comparisons were also adjusted for the cluster sampling design.
Multivariate linear regression and multivariate logistic regression analyses were used to identify risk factors for the prevalence of melanocytic nevi. The log-transformed total number of melanocytic nevi was used as the target variable for the multivariate linear regression analysis. For logistic regression analysis, number of melanocytic nevi was dichotomized by using the median (1 vs. >1) as the cutpoint.
After stable models were reached with either linear or logistic regression analysis by using stepwise selection procedures, all remaining variables were considered as potential confounders, and models were adjusted accordingly. All possible interactions between variables of one model were defined and checked for significance in hierarchical models. Results of the linear regression analysis were given as regression coefficients and 95 percent confidence intervals, whereas results of logistic regression analysis were presented as prevalence odds ratios with 95 percent confidence intervals. The results of multivariate linear and logistic regression analyses were adjusted for the cluster sampling design.
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RESULTS |
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Randomization
Overall, 393 children (60.3 percent) attended intervention centers. They were slightly younger (age 14.6 months (SD, 14.1) vs. 16.4 months (SD, 16.0)) and were less likely to be blond or fair-haired than children in the control group (61.1 percent vs. 70.7 percent) but not significantly so after adjustment for cluster sampling (p = 0.0977 and p = 0.0816, respectively). Only two significant differences were noted between children in the intervention and control groups: the proportion who had experienced at least one very painful, blistering sunburn (0 percent vs. 2 percent, respectively; p = 0.0060) and the proportion who usually wore legionnaire hats (50.1 percent vs. 39.3 percent, respectively; p = 0.0453). However, when hat-wearing practices were examined further, we found that similar proportions of children in the intervention and control groups usually wore legionnaire or wide-brimmed hats when outdoors (79.5 percent vs. 79.4 percent, respectively; p = 0.9658).
Description of all children at baseline
A total of 652 children (46.8 percent girls) attending 25 child-care centers participated, and their ages ranged from 1 to 35 months (mean = 15.3 months (SD, 13.8)) (table 2). Almost all (95.6 percent) had a fair complexion. Most children (90.2 percent) were born in the Tropics and had four Caucasian grandparents (81.8 percent). Most questionnaires (93.7 percent) were completed by the children's mothers.
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Bivariate analyses
The children spent a median of 2.3 hours (IQR = 1.2, 4.0) outside in the sun on a typical day and a median of 178.3 hours (IQR = 30, 479) outside in the sun during the warmer half of the year prior to examination (table 2). Children with more than one nevus were likely to have spent more hours in the sun on a typical day (p < 0.001) and during the warmer half of the previous year (p < 0.001) and to have spent more hours playing in water on a typical day (p < 0.001) and during the warmer half of the previous year (p < 0.001). Children whose melanocytic nevus counts were above the median were more likely to play outside in the sun almost daily during the warmer months of the year (p < 0.001). Overall, 44.3 percent of children had a history of sunburn with "redness without peeling," and more children with higher-than-median melanocytic nevus counts than other children had experienced this type of sunburn (p < 0.001). Children with higher-than-median melanocytic nevus counts also tended to have higher sunburn scores (all p < 0.001).
When asked about sunscreen use, 47.4 percent of parents reported "almost always" applying it to their child during summer, and 29.1 percent "almost always" did so in winter. Children whose parents "almost always" applied sunscreen to their skin during summer (p < 0.001) and winter (p = 0.008) had fewer melanocytic nevi than children who used sunscreen less often.
Parents of 45.8 percent of the children reported that their child usually wore a legionnaire hat outdoors and 64.9 percent usually wore a Lycra "cover-up" swimsuit during water activities. These behaviors were more common among boys (both p < 0.001).
Results of multivariate linear regression analysis
Increasing age (p < 0.001) and playing outside in the sun almost every day during the warmer months (p = 0.003) were associated with higher melanocytic nevus counts (table 3). There was a significant protective interaction (p = 0.008) for children with red hair who had experienced one or more sunburns with "redness without peeling."
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DISCUSSION |
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Sunscreen appeared to have a protective effect against melanocytic nevi. A slight, nonsignificant protective effect (odds ratio = 0.9) was detected for "almost always" wearing sunscreen when outdoors during summer, while children for whom parents applied sunscreen more than half the time during Queensland's mild winter had significantly fewer melanocytic nevi than children who wore sunscreen less often at this time of year. It is possible that the protective effect of winter sunscreen use was stronger because sunscreen use is generally lower at this time of year and is probably confined to those parents who are very careful to protect their child from the sun. In contrast, summer sunscreen use is common in this community, and it is conceivable that some of these children spend much more time outdoors as a result, thereby reducing the benefits it affords.
Although only cross-sectional, this finding supports those of a Canadian study (19) that showed that schoolchildren who used high-sun-protection-factor sunscreen developed fewer melanocytic nevi than control children did. Although regular sunscreen use reduced the incidence of melanocytic nevi in children from temperate regions with moderate ambient ultraviolet radiation, we were skeptical whether sunscreen use could be improved enough to achieve the same result in Queensland, where an estimated 90 percent (IQR = 25.5, 100) of children attending child care already wear sun-protection-factor 30+ sunscreen (S. L. H., unpublished manuscript).
When we were planning this intervention study, the only findings that showed promise for the prevention of melanocytic nevi were associated with clothing use (34, 35
). Enta (34
) reported lower mean numbers of melanocytic nevi in a cross-section of Hutterite children (a Christian sect that wears traditional clothing covering the entire body except the face and hands) in Alberta, Canada, compared with non-Hutterite children from central Alberta. Similarly, Autier et al. (35
) found fewer melanocytic nevi on the trunks of European children aged 67 years in the highest category of clothing use and more truncal melanocytic nevi among children in the highest category of sunscreen use. Given that high-UPF clothing was underutilized and is easier to use to achieve consistent broad-spectrum protection than sunscreens, which are often applied too thinly and not reapplied at appropriate intervals (6
, 7
, 36
), we chose to use clothing. This choice seems appropriate given recent reports of the correlation between the global distribution of ultraviolet A radiation and melanoma mortality rates (37
) and evidence that the carcinogenic potential of ultraviolet A radiation has been underestimated (38
).
At baseline, children in the intervention and control groups were alike except for very painful sunburns with blistering, where five controls, but no children in the intervention group, had had such an experience. The two groups were also similar in their use of sun protection, except that more children in the intervention group than controls usually wore a legionnaire hat when outdoors. This finding is probably due to ongoing recruitment, because children in the intervention group who were recruited after the clothing had been introduced into the intervention centers would have been given a legionnaire hat from the center's stockpile (provided by the investigators) to wear while at the center. Thus, the response to the question regarding the style of hat usually worn when outdoors may not reflect the baseline situation for children in the intervention group recruited into the study later but is more a measure of compliance with hat wearing in this subset of children. A more accurate assessment of baseline hat-wearing practices would have been obtained by asking about the style of hat worn at home and at child care separately. This situation could have been prevented and the management of annual examinations simplified if the population had been sufficiently large to recruit and examine the entire cohort simultaneously. However, multiple examiners would have been needed, and tracking the movement of children and staff between child-care centers would have been more difficult.
We are confident that our measures for assessing the effect of the intervention are valid and reproducible. Melanocytic nevi were counted by one experienced examiner using a standard international protocol, and there was high concordance with an experienced dermatologist who was blinded to the randomization. Site-specific sunscreen use and information about other forms of sun protection collected in parental and staff questionnaires will enable us to control for potential confounders (e.g., sunscreen use on unprotected body sites) in the final analysis.
Limitations of the study include the possibility that parents overreported their children's sun-protective practices at baseline because they were aware of our interest in sun exposure and thus reported socially acceptable behavior. Nondifferential classification such as this has the potential to bias the results toward the null hypothesis. In addition, although interaction with control centers has been minimized to avoid altering their sun-protection behavior, in keeping with the guidelines for ethical research, we have been providing the parents of children in both groups with annual feedback on the number of melanocytic nevi their child has. This practice may improve sun-protective behavior among controls and make it more difficult to detect a difference in incident melanocytic nevi between the two groups at the completion of the study. However, because we inflated our sample size beyond that required to detect a 24 percent reduction in incident melanocytic nevi, we should have sufficient power to detect a difference as small as that achieved previously using sunscreens (19) with power in excess of 80 percent, and to answer hypotheses relating to body sites (upper arms, thighs, trunk, and posterior neck) specifically protected by clothing.
In conclusion, the present findings further substantiate the relation between melanocytic nevi and sun exposure. Although it seems likely that sun protection may reduce the number of melanocytic nevi that develop during childhood (and hence the risk of melanoma), the answer to this question awaits completion of the current intervention.
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ACKNOWLEDGMENTS |
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The authors thank Judy Woosnam and Lesley Hutton for research assistance, Dr. Aurel Moise for conducting the shade audits, Dr. Juergen Bauer for his involvement in the interrater agreement study of nevi, Dr. Peter Gies (ARPANSA) for measuring the ultraviolet radiation transmission of fabrics, Dr. Madeleine Nowak for critically reviewing the manuscript and helping to reduce the word count, Cueldee clothing for manufacturing the customized garments, Stingray for providing discounted Lycra cover-up swimsuits, Robyn Gorry for maintaining the sun-protective clothing and documenting laundry volumes, and the staff and inmates at the Townsville Correctional Center for laundering the clothing.
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References |
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