2 Norwegian Institute of Public Health, the University of Oslo, and the Municipality of Oslo. All residents of Oslo born in 1970, 1960, 1955, 1940-41, and 1924-25 were invited to the survey station, and 18 770 participated (42% in men and 49% in women). The participation rate in the diﬀerent age groups is presented previously [12]. HUBRO comprised a simple physical examination including measuring of height, weight, waist and hip circumference, blood pressure and heart rate, and collection of nonfasting venous blood ana- lyzed for serum lipids and glucose. One self-administered questionnaire was part of the letter of invitation, whereas two supplementary questionnaires were handed out at the screening station and returned in pre-stamped self-addressed envelope. The questionnaires provided information on health status, symptoms, diseases, and various aspects of health behaviour—including questions about intake of food and drinks. Because subjects aged 75-76 years were not asked about cola intake, they were not included in this study. Up to two reminders were sent to the nonresponders of the survey. All procedures at the screening station were per- formed by experienced and trained personal following a de- tailed protocol. More detailed information could be found at HUBRO’s web-site: http://www.fhi.no/hubro-en. 2.2. Ethics. The study protocol was placed before the Re- gional Committee for Medical Research Ethics and approved by the Norwegian Data Inspectorate. The study has been conducted in full accordance with the World Medical Asso- ciation Declaration of Helsinki. 2.3. The Osteoporosis Substudy. As part of HUBRO, all wom- en born in 1941 (59 years of age) who had participated in a health survey in 1981 and a random sample of the other age and gender groups were selected to an Osteoporosis substudy and oﬀered measurement of bone mineral density (BMD) of the nondominant forearm. All together 2690 subjects were measured which represent 37.0% of the factual number selected to meet at the screening station. For more detailed information, see [13]. 2.4. Assessment of Bone Mineral Density (BMD). BMD was measured by single energy X-ray absorptiometry (SXA; DTX-100, Osteometer MediTech Inc., Hawthorne, Calif, USA) at both the distal and ultradistal forearm site. The region of interest was automatically identiﬁed by the com- puter. The distal site included a ﬁxed length of 24 mm of both radius and ulna, distantly starting at the point where the distance between radius and ulna is 8 mm (8 mm point). The ultradistal site included radius from the 8 mm point to the radial endplate. All the scans were reviewed by one operator, and corrections made when artefacts appeared [13]. In the present study, we have reported data only at the distal site (10–20% trabecular bone) in tables to simplify the presentation. The results of the ultradistal site are referred in the text. More details about the measurement procedures and the quality control are published before [13, 14]. 2.5. Calculation of the Dietary Index. HUBRO has ques- tions about diet items and beverages that potentially could Journal of Osteoporosis inﬂuence the bone health, such as colas and non-cola soft drinks, fruit, berries, and vegetables. Questions related to protein intake were, however, hard to appreciate and were not included in the index. The questions for intake frequency of food items had six levels of answers: 1 = rarely/never; 2 = 1–3 times per month; 3 = 1–3 times per week; 4 = 4–6 times per week; 5 = 1-2 times per day; 6 = 3 or more times per day. For beverages there were ﬁve levels: 1 = rarely/never; 2 = 1–6 glasses per week; 3 = 1 glass per day; 4 = 2-3 glasses per day; 5 = 4 or more glasses per day. The food frequency questions do not allow calculation of “true” intake frequencies or amounts, and no correction was made for variations in units, that is, 6 levels for food items (from rarely/never to 3 or more times per day) and 5 levels for beverages (from rarely/never to 4 or more glasses per day). The Dietary Index was then constructed based upon the literature about whether a food item was classiﬁed as positive or negative for bone health. We used the intake frequency levels (1 to 6 for foods and 1 to 5 for beverages) as crude estimates of intake frequencies. The index was then deﬁned as the sum of intake frequency levels of colas and non-cola soft drinks (sum of two item, range 2–10) divided by the sum of intake frequency estimates of fruit/berries, fruit juice, cooked vegetables, and raw vegetables/salads (sum of four items, range 4–23). Thus, the lowest value for the index was 0.08 and the highest value was 2.50. Thus, the rationale for calculating the dietary index was that bone mineral density is expected to be negatively related to factors in the nominator and positively to those in the denominator. It was required that all subjects of the study had values >0 for all components of the dietary index, thereby avoiding zero values for the nominator and denominator. We also calculated an alternative index, using times per week for the intake frequencies, using midpoints of the frequency intervals. For example, intake frequency 1-2 times per day would be 1.5∗7 = 10.5 times per week, and 1–3 times per month would be 2/4 = 0.5 times per week. The response alternative “rarely/never” was set to zero (actually 0.01 to be able to calculate) times per week, and “4 glasses or more per day” was deﬁned as 28 glasses per week. Thus, both the lowest and highest response alternatives would underestimate the true frequencies. In any instance, none of the approximations would give information of intake amounts, or even true intake frequencies. In the statistical analyses, we chose to include only sub- jects having data on all of the components of the Dietary Index. The material therefore consisted of 2126 subjects. The distribution of the Dietary Index was slightly skewed with the tail towards higher values. The mean values were in the range from 0.2 to 0.4 in the various age groups (Table 1). 2.6. Covariates. Body Mass Index was deﬁned as weight in kg divided by height in meter squared and was measured with- out shoes and with light indoor clothing. The questionnaires provided information about the other covariates. Smoking status was categorized as daily smokers versus nonsmokers/ former smokers. Years of education was used as a continuous variable. The question about alcohol consumption had 8 categories, from 4–7 times per week to never drunk alcohol.