People younger than 15 at the time of above-ground testing (between 1951 and 1963) who drank milk, and who lived in the Mountain West, Midwestern, Eastern, and Northeastern United States, probably have a higher thyroid cancer risk from exposure to I-131 in fallout than other people. Their thyroid glands were still developing during the testing period. And they were more likely to have consumed milk contaminated with I-131. The amount of I-131 people absorbed depends on:
- Their age during the testing period (between 1951 and 1963)
- The amount and source of milk they drank in those years
- Where they lived during the testing period
Age and residence during the Cold War years are usually known. But few people can recall the exact amounts or sources of the milk they drank as children. While the amount of milk consumed is important in determining exposure to I-131, it is also important to know the source of the milk. Fresh milk from backyard or farm cows and goats usually contained more I-131 than store-bought milk. This is because processing and shipping milk allowed more time for the I-131 to break down.