Blood Oxytocin Levels Don't Reflect Brain Oxytocin at Rest — But They Do After Stress or Nasal Spray | Research

The takeaway

Blood oxytocin measurements only correlate with brain oxytocin after stress or nasal oxytocin administration, not under resting conditions, challenging a common research practice.

r=0.08 at rest vs. r=0.66 after nasal spray
Blood oxytocin is meaningless as a brain oxytocin proxy at rest, but strongly correlated after intranasal administration — a finding that challenges widespread research practices

What the researchers found

Meta-analysis of 17 studies with 516 total participants/subjects found:

- Overall central-peripheral oxytocin correlation: r=0.29 (95% CI: 0.14-0.42, p=0.003)

- Under basal (resting) conditions: r=0.08 (p=0.31) — NO significant correlation

- After intranasal oxytocin administration: r=0.66 (p<0.0001) — STRONG correlation

- After experimentally induced stress: r=0.49 (p=0.001) — MODERATE correlation

These results indicate that central and peripheral oxytocin release are coordinated after stress or exogenous administration, but not under resting conditions. The common research practice of using blood oxytocin to approximate brain oxytocin at baseline is not supported.

Why it matters

Oxytocin is being investigated as a treatment for autism, social anxiety, PTSD, and other psychiatric conditions. Many clinical studies measure blood oxytocin as a biomarker, but this meta-analysis shows that resting blood levels don't tell us what's happening in the brain — potentially invalidating the conclusions of studies that relied on this assumption.

How the study worked

Pre-registered systematic search and meta-analysis. Databases were searched for studies reporting both central (cerebrospinal fluid) and peripheral (blood/plasma/saliva) oxytocin concentrations in the same subjects. 17 studies with 516 participants/subjects were included. Correlations were calculated overall and stratified by condition (basal, post-intranasal administration, post-stress).

What this study cannot tell us

The meta-analysis included only 17 studies with a combined 516 subjects, which is relatively modest. Many included studies used animal subjects, and results may not fully translate to human clinical populations. Central oxytocin measurement requires cerebrospinal fluid collection, which limits the types of studies that can be done. Different peripheral measurement methods (plasma, saliva, urine) may have different correlations.

How to read the evidence

This is a pre-registered systematic review and meta-analysis, representing the highest level of evidence synthesis. The pre-registration strengthens the credibility of the findings. However, the total subject pool (516) across 17 studies is modest.

When this study was published

Published in 2017, this meta-analysis continues to influence oxytocin research methodology and has been widely cited as a cautionary finding for the field.

The bigger picture

This meta-analysis has methodological implications for the entire oxytocin research field. As oxytocin-based therapies advance toward clinical use for psychiatric conditions, knowing that peripheral measurement is unreliable at baseline forces the field to develop better biomarkers or alternative methods for assessing central oxytocin activity in patients.

Questions still open

What alternative biomarkers could reliably indicate central oxytocin activity without CSF sampling?
How should clinical trials of intranasal oxytocin interpret their peripheral measurement data?
Does the stress-induced correlation mean that oxytocin research should always include stress paradigms?

Common questions

Why can't a blood test tell us about oxytocin in the brain?

Oxytocin in the blood and oxytocin in the brain appear to be regulated somewhat independently under normal resting conditions. The blood-brain barrier may prevent easy exchange, and different triggers may release oxytocin in the two systems at different times. Only when the system is activated (by stress or nasal spray) do the two levels sync up.

What does this mean for oxytocin therapy research?

It means that measuring blood oxytocin levels in patients at rest doesn't reliably indicate what's happening with oxytocin in their brain. Clinical trials testing nasal oxytocin sprays can use blood levels as a proxy (since they correlate after nasal administration), but studies trying to link baseline blood oxytocin to psychiatric conditions may have been drawing unreliable conclusions.

Read the original research

The correlation between central and peripheral oxytocin concentrations: A systematic review and meta-analysis.

Neuroscience and biobehavioral reviews, 78, 117-124

View on PubMed ↗Publisher’s paper ↗

Citation

Valstad, Mathias; Alvares, Gail A; Egknud, Maiken; Matziorinis, Anna Maria; Andreassen, Ole A; Westlye, Lars T; Quintana, Daniel S. (2017). The correlation between central and peripheral oxytocin concentrations: A systematic review and meta-analysis.. Neuroscience and biobehavioral reviews, 78, 117-124. https://doi.org/10.1016/j.neubiorev.2017.04.017