GDF-15 (Growth Differentiation Factor 15)

GDF-15, also called macrophage inhibitory cytokine-1, is released by most tissues under mitochondrial, inflammatory or hypoxic stress. It is not organ-specific, which is exactly why it predicts death so well: it integrates stress from everywhere.

Lori Daniels, Alan Maisel and Elizabeth Barrett-Connor produced the landmark cohort result in Circulation. In the Rancho Bernardo Study, 1,740 community-dwelling participants had sufficient blood for GDF-15 and 1,391 without prior cardiovascular disease entered the outcome analysis, mean age 70 plus or minus 11 years, 36% men, followed a mean 11.0 plus or minus 3.7 years to a maximum of 16.2 years [1]. Median GDF-15 was 1,370 ng/L overall (Q1-Q3 1,008-1,897), 1,740 ng/L in those with prevalent cardiovascular disease and 1,268 ng/L in those without [1]. The 95% concentration range was 634 to 2,928 ng/L, and men ran higher than women, 1,349 vs 1,229 ng/L, p = 0.001 [1].

Shanhui Xie, Liping Lu and Liwei Liu pooled 31 prospective studies covering 53,706 subjects and 7,020 adverse events. Comparing the highest GDF-15 category with the reference, the hazard ratio was 2.52 (95% CI 2.06-2.97) for all-cause mortality, 2.66 (95% CI 1.69-3.63) for cardiovascular mortality and 1.81 (95% CI 1.42-2.21) for the composite adverse outcome [2]. Per log-unit increment the figures were 2.70 (95% CI 2.29-3.12) for all-cause mortality and 2.11 (95% CI 1.57-2.66) for cardiovascular mortality [2].

Maria Conte and Claudio Franceschi showed the aging gradient directly: in 693 people aged 21 to 113, the high-mitokine elderly cluster had median GDF15 of 1,835.2 pg/mL against 952.0 pg/mL in the low cluster, p = .000, and nonagenarians in the low cluster had longer estimated survival, p = .000, and stronger handgrip, p = .007 [3]. Leila Motlagh Scholle and Stephan Zierz note GDF-15 is also used clinically to screen for mitochondrial myopathy [4].

How it is measured: immunoassay on serum or plasma. The Rancho Bernardo assay ran a measurable range of 2 to 10,000 ng/L, limit of detection 2 ng/L, intra-assay CV 7% and inter-assay CV 10% at 1,950 ng/L [1]. Note the unit trap: ng/L and pg/mL are numerically identical.

How to move it: no supplement or drug has been shown to lower GDF-15 and improve outcomes. Metformin raises it, and that rise is part of how metformin suppresses appetite, so a higher reading on metformin is not the same signal as a higher reading off it. Treat GDF-15 as a warning light, not a target to paint over.