Summary: In a small pilot study in men, eight days of intranasal vitamin C raised serum vitamin C, acutely improved the insulin response, and attenuated a decline in brain phosphocreatine in those with obesity, without changing food intake.
PICO Summary
| Element | Detail |
|---|---|
| Population | 15 men with obesity (BMI >30) and 15 normal-weight men (BMI 20–25); placebo-controlled crossover pilot study, Germany. |
| Intervention | Intranasal vitamin C 80 mg ascorbic acid daily for 8 consecutive days, with brain energy measured by phosphorus MR spectroscopy. |
| Comparison | Intranasal placebo under the same protocol. |
| Outcome | In the obese group, vitamin C acutely suppressed the physiological insulin response on day 1 (p=0.003, indicating improved insulin sensitivity), raised serum vitamin C over 8 days (p=0.011), compensated for the missing food-intake-induced vitamin C rise (p≤0.002), and attenuated a phosphocreatine decline (p=0.008). Serum vitamin C correlated with brain energy state in both groups. Food intake was unchanged. |
Expert Commentary
This is an inventive mechanistic pilot probing a genuinely interesting idea, that obesity involves impaired brain energy metabolism and lower vitamin C status, and that delivering vitamin C intranasally to bypass first-pass metabolism might address both. The findings are coherent, with improved insulin sensitivity, restored circulating vitamin C, and a blunted fall in brain phosphocreatine pointing to better cerebral energy reserve, and the use of phosphorus magnetic resonance spectroscopy to measure high-energy phosphates non-invasively is a notable strength. The honest framing, which the post maintains well, is that this is preliminary and far from clinical translation: only 15 men per group, an eight-day window, men only, surrogate neuroenergetic and acute insulin measures rather than HbA1c or clinical outcomes, and an intranasal formulation that is not commercially available. Can I use this with my patients? Not as a treatment. There is no basis here to recommend intranasal vitamin C, which patients cannot obtain anyway, and the practical takeaway is simply that vitamin C status is often suboptimal in obesity, so ensuring adequate intake is reasonable, while these intriguing brain-energy findings await larger, longer, and mixed-sex confirmation.
References
Ingwersen LC, Kistenmacher A, Melchert UH, Oltmanns KM. Metabolic and neuroenergetic effects of intranasal vitamin C application in the human brain. Nutrients. 2025;17(24):3875. doi:10.3390/nu17243875