Effect of a low-fat diet on hormone levels in women with cystic breast disease. II. Serum radioimmunoassayable prolactin and growth hormone and bioactive lactogenic hormones.

For investigation of the bioactivity of circulating prolactin and growth hormone (lactogenic hormones) in symptomatic benign breast disease, serum was assayed by the Nb2 lymphoma cell method in premenopausal patients with cystic breast disease and cyclic mastalgia and in normal premenopausal women. The results were compared with serum prolactin and growth hormone concentrations determined by radioimmunoassay. The serum bioassayable hormone levels in the benign breast disease patients (74.0 +/- 77.6 ng/ml) were significantly higher (P less than .001) than in normal women (23.8 +/- 10.7 ng/ml). There were no significant differences in the radioimmunoassayable prolactin or growth hormone levels between the 2 groups. When 16 cystic breast disease patients were placed on a low-fat (20% of total kilocalories) diet for 3 months, there were significant reductions in the serum bioassayable hormone levels (P less than .02). It is concluded that the bioactivity of prolactin may be elevated in the serum of patients with cystic breast disease and cyclic mastalgia, without corresponding increases in levels determined by radioimmunoassay; that this abnormality is reversible by a reduction in dietary fat consumption to 20% of the total kilocalories; and that serum prolactin may provide a valuable biomarker in clinical trials of a low-fat diet in women at high breast cancer risk.