NAD and the Ageing Brain: Part Four: NAD and the Clock

Abstract

The strongest remaining claim for NAD+ in the ageing brain is not about energy. It is about time.

A review published in Alzheimer's & Dementia in 2026 sets out a bidirectional relationship between NAD+ metabolism and the circadian clock: the clock regulates NAD+ synthesis, and NAD+-dependent signalling feeds back onto the clock. Both degrade in dementia.

This part covers that argument, which is the most mechanistically specific reason to expect NAD+ precursors to affect sleep rather than to affect everything. It also covers why the same argument points away from supplements.

1.The Clock, Briefly

Light entrains the master circadian pacemaker in the suprachiasmatic nucleus of the hypothalamus, which regulates autonomic output and drives nocturnal melatonin synthesis in the pineal gland.

Sleep and wakefulness are governed by a reciprocally inhibitory switch: the ventrolateral preoptic area suppresses arousal centres during sleep through GABAergic and galaninergic neurons, while orexin neurons in the lateral hypothalamus provide excitatory drive during wakefulness and limit inappropriate state transitions.

At the molecular level the clock runs on transcriptional feedback loops. CLOCK and BMAL1 form heterodimers that bind E-box elements in target gene promoters and initiate transcription in a circadian pattern.

In dementia, the review describes weakening output from the suprachiasmatic nucleus, diminished circadian amplitude, fragmented sleep and blunted daily activity — alongside dysregulated clock-gene expression and falling levels of circadian-related metabolites including NAD+.

2.Where NAD+ Enters

The coupling runs through four named components, and the specificity is what distinguishes this from a general appeal to cellular energy.

Nicotinamide phosphoribosyltransferase — NAMPT — drives the salvage pathway that regenerates NAD+ from nicotinamide. Its expression is itself under circadian control, which makes NAD+ availability an oscillating quantity rather than a constant one.

NAD+-dependent sirtuin signalling, principally SIRT1, feeds back onto the transcriptional-translational feedback loop that constitutes the clock. Energy status and timekeeping are therefore not separate systems.

And NAD+ is consumed by PARP1, activated by DNA damage, and by CD38, which rises with age and inflammation. Both draw down the same pool the clock depends on.

The authors are careful about the status of this map. Their own highlights state that key links between NAD+ signalling and the clock components are summarised with interactions requiring further confirmation highlighted, and that the mechanisms are synthesised for further exploration. This is a framework, presented as one.

3.Why This Is the Best Version of the Claim

Most NAD+ marketing rests on a generic argument: cellular energy declines, NAD+ is central to energy, therefore restoring NAD+ helps. That reasoning predicts improvement in everything, which is why it survives contact with results like those in Part Two — nothing was specifically predicted, so nothing was specifically refuted.

The circadian argument predicts something narrower. It says the effect should appear in the timing and architecture of sleep, in a population whose clock is degrading, and it identifies the enzymes through which that would happen. Narrow predictions can fail, which is what makes them worth testing.

It also explains a puzzle from Part Two. If NAD+ acts primarily on circadian regulation, then measuring grip strength and gait speed in unselected older adults would be looking in the wrong place, and would return exactly the nulls that were found.

4.The Part That Cuts the Other Way

The review's own list of strategies targeting NAD+ contains supplements and a good deal else: modulators of NAD+ biosynthetic and depleting enzymes, timed light and activity exposure, structured exercise programmes, and dietary interventions.

The introduction goes further, stating that maintaining sleep continuity and following regular timing of light exposure, activity and meals are core strategies for preserving cognitive resilience and delaying dementia.

That sentence names light, activity and meal timing as core. Not precursor supplementation. If the circadian account is correct, the interventions with the strongest evidence and the largest effects are behavioural, and they are free.

A supplement can be worth testing within a framework whose main practical implications are not about supplements. Both things are true here and only one of them tends to get quoted.

5.What Would Test It

The review registers five ClinicalTrials.gov identifiers, one of which is the Buffalo sleep trial covered in Part Five.

A proper test of the circadian hypothesis would need three things this literature does not yet have: an objective measure of sleep architecture rather than a questionnaire, a population with demonstrable circadian disruption rather than unselected older adults, and confirmation that NAD+ actually rose in the participants studied.

Part Five describes two trials, each of which has some of that and neither of which has all of it.

Editorial Comment

MindHeaven® makes no claim that NAD+ or any precursor affects sleep, circadian rhythm or cognition. None is authorised in the European Union.

We publish this part because it is the strongest case that can be made for the compound family, and a series that only presented weak versions of an argument would not be worth reading. The circadian coupling described here is specific, mechanistically detailed and testable.

It is also, on the review's own account, a framework awaiting confirmation, in which the best-supported interventions are light, activity and meal timing. If you take one practical thing from this part, it should be that one.