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Journal of the American College of Nutrition, Vol. 17, No. 5, 454-457 (1998)
Published by the American College of Nutrition

Dietary Caffeine Intake Is Not Correlated with Adolescent Bone Gain

Tom Lloyd, PhD, Nan Johnson Rollings, RN, MEd, Kessey Kieselhorst, MPA, RD, Douglas F. Eggli, MD and Elizabeth Mauger, PhD

Departments of Obstetrics and Gynecology (T.L., N.J.R.), Penn State College of Medicine and University Hospitals, The Milton S. Hershey Medical Center, Hershey, Pennsylvania
Department of Radiology, (D.F.E.), Penn State College of Medicine and University Hospitals, The Milton S. Hershey Medical Center, Hershey, Pennsylvania
Department of Clinical Nutrition (K.K.), Penn State College of Medicine and University Hospitals, The Milton S. Hershey Medical Center, Hershey, Pennsylvania
Health Evaluation Sciences (E.M.), Penn State College of Medicine and University Hospitals, The Milton S. Hershey Medical Center, Hershey, Pennsylvania

Address reprint requests to: Tom Lloyd, PhD, Department of Obstetrics and Gynecology, The Milton S. Hershey Medical Center, Hershey, PA 17033


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Objective: This study was conducted to determine whether dietary caffeine consumed by American white females between ages 12 to 18 affects total body bone mineral gain during ages 12 to 18 or affects hip bone density measured at age 18.

Methods: The Penn State Young Women’s Health Study is a longitudinal investigation of bone, endocrine and cardiovascular health in non-Hispanic, white, teenage women. Nutrient and food group intakes were obtained by averaging over 6 years of prospective diet records. The cohort, as of age 18, (n = 81) was separated into three subgroups according to mean daily caffeine intake averaged across ages 12 to 18. Group I (n = 37) consumed less than 25 mg caffeine per day; Group II (n = 33) consumed 25 to 50 mg caffeine per day; and Group III (n = 11) consumed greater than 50 mg caffeine per day. The group mean daily caffeine intakes (SD) were Group I = 14 (6) mg/day; Group II = 35 (7) mg/day; Group III = 77 (27) mg/day. Total body bone gain and hip bone density were determined by dual energy x-ray absorptiometry (DXA).

Results: There were no significant differences among the three caffeine intake groups for total body bone mineral gain during the ages 12 to 18 or of hip bone density at age 18. The low caffeine intake group consumed more milk (and therefore more calcium) and more fruit per day than did the other two groups. Group III, the highest caffeine intake group, consumed more sugar per day than did the other two groups. The observed differences in nutrient and food intakes among the three groups were not associated with any differences in anthropometric measurements or bone gain among the three groups.

Conclusion: These findings indicate that dietary caffeine intake at levels presently consumed by American white, teenage women is not correlated with adolescent total bone mineral gain or hip bone density at age 18.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Osteoporosis is a major public health problem, and the lifetime risk of hip fracture for United States women at the age of 50 years is about 17% [1]. This risk increases dramatically after age 70. Osteoporotic bone is characterized by changes in microarchitecture and decreased bone density resulting in greater susceptibility to fracture. Bone density at any time of adult life is the result of peak bone density achieved at the end of adolescence and subsequent lifelong bone loss [2]. Since approximately 40% of women’s adult skeletal mass is gained during the ages of 12 to 18, modifiable lifestyle factors that affect bone gain in adolescence are of great importance [3,4].

Dietary caffeine intake has been proposed and refuted as a determinant of bone density, bone mass and fracture risk in adult women [5–19]. Caffeine is recognized as a mild diuretic and short-term increases in urinary calcium excretion have been observed, accompanying temporary increases in sodium excretion [20,21]. These effects are small, transient and have little effect on the calcium economy [14]. Past epidemiologic studies examining relationships among calcium, bone density and fracture frequency have been conducted in postmenopausal women [5–15], with fewer studies of premenopausal women [16–19]. The elegant balance studies by Heaney and coworkers demonstrate small but statistically significant inverse effects between dietary caffeine and calcium excretion among adult women ages 35 to 69 years [14]. However, to our knowledge, the effects of caffeine on bone mass and bone gain during adolescence in healthy, teenage women have not been previously examined.


   METHODS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
The database from The Penn State Young Women’s Health Study, which was begun in 1990 when the subjects were 12 years old, was used for this analysis. The study population is representative of white females attending public school in central Pennsylvania and was limited by design to descendants of Northern Europeans. We previously reported details of the recruitment and retention strategies; baseline anthropometric, endocrine and bone measurements; and effects of a calcium supplementation trial on adolescent bone gain [22,23]. The present analysis was performed when members of the cohort were 18.1 (0.5 SD) years of age. The 6-year nutrient intake and bone density measurements for the 81 members of the cohort who remained in the study during this period were used in the analysis. All procedures were reviewed and approved by the Pennsylvania State University College of Medicine Institutional Review Board, and all subjects and their parents provided informed consent.

Anthropometric Measurements
All subjects were seen individually by the research coordinator (NJR) who measured height and weight, obtained Tanner Stages, and reviewed diet records as previously described [22,23].

Nutrient Intake Assessment
Prospective 3-day diet records were completed at baseline and then every 6 months during ages 12 to 16 by each subject with parental help as needed. Thereafter (ages 17 and 18), nutrient assessment was performed yearly. The diet records were analyzed with Nutritionist III (Version 7.0) software to obtain nutrient intake measurements [24]. The major sources of caffeine for children and teenagers are carbonated beverages, chocolate-containing foods and tea beverages. The Nutritionist III (Version 7.0) program takes into account the caffeine content of all of these sources. Each individual’s average daily intake for each nutrient and caffeine was calculated as the average for each subject for the 6 years of data for each variable. These 6-year average daily values were then used in the analysis.

Bone Mineral Measurements
All bone mineral content (BMC) and integral bone mineral density (BMD) measurements were made with Hologic Dual Energy X-Ray Bone Absorptiometers (QDR-1000W and QDR-2000W Hologic, Waltham, Massachusetts). During the first 4 years, (ages 12 to 16) each subject had total body scans made every 6 months. Thereafter, scans were made yearly. In addition to the total body scans made with the pencil beam mode (ages 12 to 18), both hips were scanned at age 18 using the array mode. The 6-year total body bone mineral gains were calculated by subtracting the age 12 measurements from the age 18 measurements. The details of this method and its reproducibility have been reported [25–28].

Study Groups
Adolescent women in the United States obtain the majority of their caffeine intake from cola beverages [29,30] which contain, on average, 30 mg caffeine/12 oz [29]. Accordingly, the intake boundaries of the three caffeine groups were set to reflect average daily consumption of less than one cola per day (Group I), one to two colas per day (Group II), or more than two colas per day (Group III).

Statistical Analyses
Statistical procedures were accomplished using a range of procedures for SAS [31]. We summarized the baseline characteristics as an average for each caffeine group. These averages were then compared using the analysis of variance (ANOVA) model. The bone measures and average daily nutrient intakes for each caffeine group were also compared using an ANOVA model.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
The mean daily caffeine intakes over the 6-year interval (ages 12 to 18) for the three caffeine study groups were as follows: Group I (n = 37) 14 ± 6 mg/day; Group II (n = 33) 35 ± 7 mg/day and Group III (n = 11) 77 ± 27 mg/day. As shown in Table 1, there were no differences or trends among the physical measurements of the subjects among the three caffeine study groups.


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  		Table 1. Physical Statistics of the Three Caffeine Groups at Age 18

 
The total body bone mineral content gain and hip bone density measurements of the three caffeine study groups are shown in Table 2. No group to group differences or trends were observed. As expected, between the ages of 12 and 18, all members of the cohort gained approximately 40% of their adult skeletal bone mass gaining, on average, approximately 900 g of total body bone mineral. There was no difference among the three caffeine groups in hip bone density at age 18 as illustrated by the p-values (based on ANOVA) of 0.93–0.96.


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  		Table 2. Bone Measurements of the Three Caffeine Groups

 
As indicated in the Methods section, nutrient intake data were obtained by averaging the values obtained from the 11 3-day diet records completed between ages 12 and 18. The major food groups and specific nutrient intakes of the three caffeine groups were then compared with the ANOVA model and are presented in Table 3. There were statistically significant differences for the average intake of calcium, sugar, bread, milk, and fruit among the three groups. No observed trends in consumption patterns were found among the three groups for milk, calcium, sugar, and bread.


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  		Table 3. Selected Food and Nutrient Intakes of the Three Caffeine Groups

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
To put our findings into context, we will 1) summarize findings from observational studies on dietary caffeine intake, bone density and fracture frequency; 2) summarize findings on the effect of caffeine on calcium balance in adult women; and 3) compare our results to other observational reports on the relationships among caffeine intake in young women and bone density and fracture frequency.

The several recent studies on the relationships among caffeine intake, bone density and fracture risk among postmenopausal women generally demonstrate that the equivalent of eight cups of coffee per day is not a risk factor for bone loss in otherwise healthy postmenopausal women [4,7,8,10]. However, in other studies, relative risk factors of 1.2–1.5 for caffeine intake and osteoporosis risk have been reported [5,6,9,12].

The present analysis was conducted to assess the effect, if any, of adolescent caffeine consumption on peak skeletal mass acquisition. To our knowledge, there are no interventional studies dedicated to assessing the effect of caffeine on human skeletal bone. Several studies support the general concept that young women increase their caffeine consumption as they advance through adolescence. In the present study, cola beverages and tea-coolers were the dominant caffeine sources. Less than 10% of the study cohort were drinking coffee on a daily basis by age 18. For this cohort of 81 white females, average daily caffeine intake between ages 12 to 18 was 31 ± 23 mg/day with a range of 4 to 146 mg/day. In a cross-sectional secular analysis, it was observed that white girls in the Bogalusa study increased their average caffeine consumption from 62 mg/day at age 10 to 104 mg/day at age 15 [32].

Packard and Recker studied modifiable determinants of bone gain among 145 women who were in their early 20’s and observed that caffeine intake (mean value: 103 ± 106 mg/day; range: 7–809 mg/day) was not associated with bone gain. These investigators observed that bone gain was positively correlated with physical activity and calcium intake and negatively correlated with age and protein intake [18]. Wyshak and Frisch reported that higher consumption of cola beverages, but not caffeine, was correlated with increased likelihood of bone fractures among 14 year old girls but not among 14 year old boys [19]. The subjects were recruited from athletic clubs and from orthopedists’ outpatient offices. Since 30 of the 76 girls and 21 of the 51 boys reported at least one fracture by mid-adolescence, it is likely that this cohort was at great risk for fracture due to their athletic activities. The results of the present study indicate that typical caffeine consumption during adolescence is not correlated with bone gain during ages 12 to 18 or with hip bone density at age 18 among white teenage women.


   ACKNOWLEDGMENTS
 
This study was supported by PHS Grants R01-HD 25973 and M01-RR-10732.

Received December 1, 1997. Accepted April 1, 1998.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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