The Janus samples originate from three different sources. In the 1970s–90s, a number of population-based health surveys for monitoring risk factors for cardiovascular diseases, were performed in Norway. About 90% of the Janus donors were recruited from five of those health surveys. Approximately 10% of the Janus cohort members origin from Red Cross blood donors living in Oslo and the surroundings. A small proportion of the samples (n ∼ 3 500) in the cohort are from donors that entered the cohort with a pre-diagnostic sample at one time point, were later diagnosed with cancer and donated a new diagnostic sample. For this subgroup, both pre-and post-diagnostic samples from the same individuals are available. See the table below for details.
| Characteristics | Men | Women | Total |
| Total donors included in the cohort | 166137 | 152491 | 318628 |
| Average age at enrolment (years) | 41 | 41 | - |
| Number of individuals by sample origin | |||
|
- Health Examination donors (Oslo 1, The Age 40 program Oslo, The Norwegian Counties Study, The Age 40 program all counties and TROFINN) |
146222 | 134898 | 281120 |
| - Red Cross Blood donors | 15079 | 13811 | 28890 |
| Number of donors by number of sample collection time points | |||
| Health examination donors | |||
| 1 | 118707 | 108067 | 226774 |
| 2 | 17524 | 16082 | 33606 |
| 3 | 9457 | 10117 | 19574 |
| 4 | 534 | 632 | 1166 |
| Red Cross Blood donors | |||
| 1 | 5213 | 5971 | 11184 |
| 2 | 3066 | 2940 | 6006 |
| 3 | 1929 | 1620 | 3549 |
| 4 | 4871 | 3280 | 8151 |
Geographical distribution of sample collection in the Janus Serum Bank
