Effects of an oral mixture containing glycine, glutamine and niacin on memory, GH and IGF-I secretion in middle-aged and elderly subjects

42 people drank a 10g mixture of glycine, glutamine and niacin daily for 3 weeks saw an increase in serum growth hormone (GH) levels by 70%, but this GH increase was not associated with improvement in mood or memory. Circulating Insulin-like growth factor 1 (IGF-I) levels did not change.

Overview

This 2003 clinical trial (Arwert et al., Journal of Nutritional Biochemistry) tested whether an oral mixture of glycine, glutamine, and niacin could raise growth hormone (GH) levels and improve cognitive function in middle-aged and elderly adults. The three-component combination was chosen because each ingredient has independently been reported to stimulate GH secretion through distinct mechanisms.

42 healthy participants aged 40–75 received 10 grams of the mixture daily for three weeks. The primary outcomes were serum GH, IGF-I, and performance on standardized memory and mood assessments.

Key Findings

Growth hormone increased by roughly 70%. This is a meaningful effect. GH secretion declines sharply with age; interventions that restore even partial GH output are of significant interest in aging research. The effect appeared to hold across the age range studied.

IGF-I did not change. IGF-1 is the downstream mediator of most of GH’s anabolic and neurological effects — it is the signal that GH triggers the liver to produce. The absence of IGF-I change is the study’s central finding to explain. Possible reasons include: the three-week window was insufficient for hepatic adaptation; baseline IGF-I levels were already at a ceiling; or the GH pulses generated were too brief to sustain hepatic IGF-I synthesis.

No improvement in memory or mood. Cognitive and psychological outcomes showed no statistically significant changes. The authors attribute this to the absent IGF-I response: since IGF-I appears to mediate GH’s neurological benefits, a GH increase without downstream IGF-I elevation may not translate to functional brain effects.

Why Glycine, Glutamine, and Niacin?

Each component targets a different node in the GH-regulatory axis:

Glycine is an inhibitory neurotransmitter that may modulate hypothalamic GH-releasing hormone (GHRH) signaling. It is also studied for improving slow-wave sleep quality — significant because the body’s largest GH pulse occurs during deep sleep.

Glutamine is the most abundant amino acid in circulation and a precursor for several neurotransmitters. Some studies report it stimulates GH secretion, possibly by influencing hypothalamic pH or GHRH release.

Niacin (nicotinic acid) suppresses circulating free fatty acids (FFAs). FFAs are established inhibitors of GH secretion — they exert negative feedback on GH pulses. By activating GPR109A in adipocytes and acutely reducing lipolysis, niacin lowers the FFA brake on GH release. This is the clearest and most mechanistically supported component of the combination.

Together, the three ingredients address multiple points in GH regulation simultaneously rather than relying on a single pathway.

Limitations

The trial was small (42 subjects), open-label (no placebo arm), and short (three weeks). Without a control group, the GH increase cannot be definitively attributed to the mixture rather than regression to the mean or expectation effects. The lack of IGF-I and cognitive response substantially limits the practical interpretation of the GH finding.

Relevance to Niacin Research

For researchers focused on niacin specifically, this study documents niacin’s ability to modulate GH secretion through FFA suppression — an indirect but mechanistically coherent pathway. Niacin’s inhibition of adipose lipolysis (the mechanism behind both the flushing response and the lipid-modifying effects) is sufficient to meaningfully reduce the FFA signal that inhibits GH release.

The GH-without-IGF-I finding also adds nuance to discussions of GH optimization: raising GH alone may not be sufficient to produce the downstream benefits (lean mass, cognitive function, recovery) that researchers associate with GH. The GH–IGF-I axis functions as a unit. Interventions that raise GH without moving IGF-I may be acting too far upstream, or too briefly, to generate the physiological effects of interest.