Brain fog has many causes, but cellular energy deficit in neurons is one of the most underappreciated. Here is what the NAD+ research shows about cognitive function and why it matters.

Brain fog is one of the most commonly reported yet least precisely defined symptoms in medicine. Patients describe it as mental cloudiness, difficulty concentrating, slowed thinking, word-finding problems, or a general sense that their mind is not running at the speed it used to. It can be caused by many things, including sleep deprivation, thyroid dysfunction, depression, hormonal changes, and chronic stress.

One of the less commonly discussed contributors is cellular energy deficit in the neurons themselves, and this is where NAD+ enters the picture in a specific and mechanistically grounded way.

The brain accounts for roughly two percent of body weight but consumes approximately 20 percent of the body's total energy. Neurons run almost entirely on glucose-derived ATP produced in mitochondria, and they run on it continuously. There is no energy reserve system in neurons the way there is in muscle tissue. When mitochondrial function is compromised, neuronal function suffers directly and quickly.

NAD+ sits at the center of mitochondrial energy production as the primary electron carrier in the oxidative phosphorylation chain. When NAD+ levels are adequate, the electron transport chain runs efficiently and ATP production is robust. When NAD+ is depleted or reduced, mitochondrial efficiency drops and cells produce less energy.

Neurons, with their extraordinary energy demands and no backup fuel system, are among the cells most sensitive to NAD+ insufficiency. This is the mechanistic link between NAD+ decline and cognitive symptoms.

NAD+ levels in brain tissue decline with age, consistent with what is seen in other tissues. Research measuring NAD+ in cerebrospinal fluid and brain tissue samples has confirmed progressive decline from early adulthood onward. In parallel with this, the clearance systems that remove metabolic waste from the brain (the glymphatic system, which operates primarily during sleep) become less efficient.

Animal studies have consistently shown that restoring NAD+ levels in aged brains improves mitochondrial function in neurons, reduces neuroinflammation, and produces measurable improvements in cognitive performance on memory and learning tasks. The effect sizes in these studies are meaningful and consistent across multiple research groups.

Human data on NAD+ and cognitive function is more limited but developing. A 2020 study in Aging Cell found that nicotinamide riboside supplementation in older adults reduced levels of neuroinflammatory markers in cerebrospinal fluid. A 2022 trial found improvements in fatigue and cognitive function scores in adults over 40 who supplemented with NMN compared to placebo. These are not definitively established effects, but they are consistent with the mechanistic picture.

For patients on EllieMD's longevity program who report cognitive symptoms including fatigue and mental cloudiness alongside physical signs of aging, NAD+ support is one of the most mechanistically coherent interventions available. It targets the cellular energy deficit that may be underlying the symptoms directly.

It is also worth noting that brain fog has multiple potential causes, and NAD+ support addresses one specific pathway. Thyroid function, sleep quality, stress levels, cardiovascular health, and hormonal status all affect cognitive performance. A thorough evaluation by your physician that identifies which factors are most relevant to your picture produces better outcomes than reaching for any single intervention.

For patients already experiencing benefits from sermorelin's effects on sleep quality, the combination of improved sleep and NAD+ support addresses two significant contributors to cognitive energy from different angles. Your EllieMD physician can discuss whether this combination fits your specific situation.

Patients who respond to NAD+ therapy in the cognitive domain tend to describe the effect as subtle rather than dramatic. The mental fog that was previously a background feature of their daily experience becomes less pervasive. Word retrieval feels easier. Sustained focus on tasks is less effortful. Energy in the latter half of the day, which often drops in ways that feel like the brain is running out of fuel, stays more consistent.

These are not dramatic transformations. They are the kind of functional improvements that reflect underlying cellular energy production working more efficiently. If you are expecting a noticeable pharmacological high, that is not the mechanism. If you are expecting a gradual restoration of cognitive function that reminds you of how your mind worked several years ago, that is more consistent with what the NAD+ biology and clinical experience suggest.

Individual results may vary. All prescriptions require approval by a licensed medical provider. Compounded medications are not FDA-approved. EllieMD facilitates access to independent healthcare providers and pharmacies and does not provide medical care or dispense medications.