Researchers have observed that girls who are leaner at age seven are at higher risk of cancer later in life.
The finding has been published in BioMed Central's open access journal Breast Cancer Research.
Jingmei Li worked with a team of researchers from the Karolinska Institutet, Sweden, to study the relationships between childhood body size and tumour characteristics in a group of 2,818 Swedish breast cancer patients and 3,111 controls.
She said, "Our main finding was that a large body type at age seven years was associated with a decreased risk of postmenopausal breast cancer. Although strongly associated with other known risk factors such as age of menarche, adult BMI and breast density, size at age seven years remained a significant protective factor after adjustment for these other issues".
Size at age seven was also found to determine tumour characteristics, in particular, estrogen receptor status. A large body size at age seven was especially protective against estrogen receptor negative tumours, which generally fare worse in terms of prognosis. The researchers' classification of childhood body size was derived from nine numbered pictograms ranging from very skinny (S1) to very fat (S9). Subjects assessed their own body type at present and how they remembered themselves at seven years old. These selections were then used to group them as lean (S1 to S2), medium (S3 to S4) and large (S5 to S9).
Li said, "It appears counterintuitive that a large body size during childhood can reduce breast cancer risk, because a large birth weight and a high adult BMI have been shown to otherwise elevate breast cancer risk. There remain unanswered questions on mechanisms driving this protective effect".