Untill 1985, vitamin D fortification of margarine was mandatory (1.25 µg/100g), and from 1972-76 fortification of low fat milk (2.5-3.8 µg/100g milk) was permitted. Around 15% of dietary vitamin D is estimated to have come from the fortified margarine, while the amount from milk is unknown.

The D tect study is possible due not only to these well-defined adjacent time windows but also to the complete registration of every citizen in Denmark via a civil registration number. This number can be linked, on an individual level, to Danish birth, patient and medical registries; social and ethnic registries; and clinical and other large databases. The study therefore includes approx. 3 mio individuals from nationwide birth cohorts born from 1930-90.

More specifically, the following outcomes, and respectively, national register data, will be utilized in D tect.

Using the civil registration numbers, individuals will be individually linked to the Danish National Patient Registry for incident and recurrent diseases. The register contains information about hospital contacts, including diagnosis codes and procedure codes for all treatment at Danish hospitals. From 1977-1993 diagnoses were classified according to the WHO International Classification of Diseases (ICD-8) and from 1994 ICD-10. The main study outcome is fracture of the forearm, wrist or scaphoid bone (ICD-8: 813,814; ICD-10: S52, S62.0); fracture of the clavicle (ICD-8: 810; ICD-10: S42.0); and fracture of the ankle (ICD-8: 824; ICD-10: S82.5, S82.6, S82.8).

Type 1 diabetes (T1D)
The Danish Childhood Diabetes Registry covers all children age 0-15 at diagnosis with T1D. The registry covers all patients born since 1981.

Childhood overweight and obesity
The Copenhagen School Health Record Registry (SHR) includes every student in Copenhagen Municipality since birth year 1930 through 1989 and comprises more than 350,000 records, which have been computerized for research purposes. Overweight and obesity are calculated from weight and height, which were measured annually until 1984 starting at age 6-7 and ending at age 13-14. The SHR comprises approx. 10% of all Danes from each birth cohort. Birth weight, birth complications, gestational diabetes, pre-pregnancy weight and gestational and maternal age are retrievable from the National Birth Registry. Data are available from 1973 onward.

Education, unemployment, income and ethnicity
This information will be obtained from the Statistics Denmark Fertility Database, which includes information on subjects of fertile age born since 1930 who still reside in Denmark. Social information is available for anyone born since 1981.

Vitamin D status (25(OH)D3)
Since May 1, 1981, routinely collected neonatal DBS samples taken by heel prick 48-72 hours after birth have been collected for all newborns in Denmark. After routine screening for congenital disorders, residual DBS cards are stored in the Biological Specimen Bank for Neonatal Screening at State Serum institute. Punches of stored surplus card samples will be used to measure neonatal 25(OH)D3. The assay detection method is a highly sensitive liquid chromatography tandem mass spectroscopy coupled with multiple reactant monitoring. Previous studies have shown that storage times of more than 20 years do not bias inter-individual variation in concentrations for a given birth cohort.

Get more information about the project on: http://www.D-tectingdisease.dk