If you've crossed 35 and your energy stopped showing up the way it used to, this isn't in your head — and it's not just your hormones. There's a third thing happening at the cellular level. We pulled the research and translated it.
You wake up, you have your coffee, you do the thing. By 2pm you're done. Not the kind of tired you can sleep off. The kind that feels like your battery just doesn't hold a charge anymore.
If you've been Googling "why am I so tired" and getting handed iron pills, magnesium, ashwagandha, and the same six "sleep hygiene" tips, you're not crazy. You're also not necessarily deficient in iron, low on magnesium, or doing your nighttime routine wrong.
There's a different conversation happening in the longevity science world right now — and it has a name.
It's called NAD+. And after age 35, your body starts running out of it.
This post is the science behind that drop. Not the marketing version. Not the influencer version. The actual peer-reviewed research version, with citations from the National Institutes of Health and major academic publishers — and what the data says (and just as importantly, what it doesn't say) about doing something about it.
Because once you understand what's happening at the cellular level, the conversation about your energy, your sleep, your metabolism, your perimenopause symptoms — all of it — gets a lot more useful.
First — What NAD+ Actually Is (and Why It Matters)
NAD+ stands for nicotinamide adenine dinucleotide. (You don't have to remember that.)
Think of it as the cellular currency that powers basically everything. Every cell in your body uses NAD+ to convert food into energy, repair its own DNA, and communicate with its mitochondria — the little engines inside cells that produce ATP (which is the actual fuel your muscles, brain, and organs run on).
Without enough NAD+, mitochondria stop working efficiently. When mitochondria slow down, you feel it as: low energy, brain fog, slower recovery, harder weight loss, worse sleep quality, less resilient immune function, and a general sense that your body just isn't responding the way it used to.
Here's the kicker: this isn't optional. NAD+ is required for over 500 enzymatic reactions in the human body. It's not a vitamin you can skip. It's infrastructure.
The cellular currency you've never heard of
Most people have heard of CoQ10. Most people have heard of B vitamins. Almost nobody has heard of NAD+ — even though it's arguably more important than either, because B3 (niacin) is one of NAD+'s building blocks.
Why hasn't it been on your radar? Because for a long time, the science was complicated and the supplementation options were limited. The research has caught up, and the delivery options (nasal sprays, IV, injectable, oral precursors) have caught up. The conversation just hasn't reached most women yet.
That changes today.
The Decline That Hits Hardest After 35
Here's where the research gets specific.
A 2016 paper published in Cell — one of the most cited journals in biology — quantified what happens to NAD+ as we age. By middle age, NAD+ levels in human and animal tissues drop to roughly half of what they were in youth. In skin samples, the average NAD+ concentration decreases at least 50% over the course of adult aging.
That's not a slow trickle. That's a meaningful, measurable cliff.
How fast does NAD+ actually drop?
The current best estimate from peer-reviewed research is that NAD+ declines steadily across adulthood, with a noticeable acceleration around midlife. Multiple studies in mice — and increasingly in human samples — show twofold reductions in NAD+ levels in tissues including liver, skeletal muscle, and skin by middle age.
If you've felt like something shifted in your mid-to-late 30s — like you weren't recovering from workouts the same way, or your skin was changing without warning, or your sleep stopped feeling restful — the timeline lines up. That's not coincidence.
The villain in the story: an enzyme called CD38
Here's the part most NAD+ articles skip, and it's actually the most interesting piece.
Your NAD+ doesn't just "decline" passively. It gets actively destroyed by an enzyme called CD38.
CD38 is an enzyme that lives on the surface of certain immune cells. Its job is to break down NAD+. As you age, the body produces more CD38 — partly because chronic low-grade inflammation increases with age (the technical term is "inflammaging") and CD38 is part of the inflammatory response.
Research from major university labs has shown that mice engineered to lack CD38 are protected from age-related NAD+ decline AND from mitochondrial dysfunction. In other words: less CD38 = preserved NAD+ = better cellular function. (This isn't a license to start hacking your CD38 — but it explains the mechanism.)
The translation for you: aging-related inflammation directly drives NAD+ destruction. So managing inflammation isn't a separate health goal from managing your energy. They're the same goal.
Why Women in Perimenopause Feel It Hardest
Here's where this gets specifically relevant for the woman reading this who's already wondering if she's losing her mind.
Age-related NAD+ decline overlaps directly with the hormonal transitions of perimenopause and menopause. And not in a small way.
The hormonal acceleration
Estrogen plays a role in regulating cellular energy production. As estrogen levels begin to fluctuate and drop in perimenopause (which can start as early as your mid-30s), mitochondrial efficiency takes a hit at the same time NAD+ is naturally declining.
Translation: you're getting hit with two metabolic headwinds at the same time. The cellular energy infrastructure is breaking down (NAD+ decline) AND the hormonal signal that keeps it running smoothly is changing (estrogen shifts).
That's why women in perimenopause often describe their fatigue as different from regular tired — it's a deeper, more systemic version. Because the cellular machinery itself is running on reduced inputs.
The symptoms that get blamed on stress
Women experiencing this combination often get told one of three things by their providers:
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"You're stressed."
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"It's just your hormones."
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"It's normal at your age."
All three of those things might be partially true, and none of them are particularly useful.
The real picture is more specific: as NAD+ drops and estrogen shifts, you may experience:
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Persistent afternoon energy crashes that don't respond to caffeine
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Sleep that doesn't feel restorative even when the hours look fine on paper
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Slower workout recovery and harder strength gains
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Brain fog, especially around 2–4pm
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Skin changes — duller texture, less bounce-back, slower wound healing
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Weight that gathers around the midsection in ways it never used to
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Mood changes that feel "off" but don't quite fit a depression diagnosis
If that list reads like your last six months — your cells might be telling you something.
What the Research Actually Shows About NAD+ Supplementation
Now, the responsible part. Here's what the science currently says about whether you can DO anything about all this — and where the science still has gaps.
Where the research is strongest
Multiple peer-reviewed studies on NAD+ precursors (the building blocks your body uses to make NAD+, including NMN and NR) have shown:
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Increased NAD+ levels in human blood and tissues with consistent supplementation
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Improved muscle insulin sensitivity in clinical trials of overweight prediabetic women
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Improvements in subjective measures of energy, sleep quality, and recovery in some studies
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In one published study, women on NAD+ precursor supplementation reported decreases in bloating frequency, improvements in hot flash frequency, and improvements in poor-sleep frequency
The honest caveats (because we're in this for the long game)
Most of the dramatic NAD+ research has been done in mice. Human studies are growing fast but are still smaller and shorter than we'd like. The effects in humans tend to be subtler and slower than the marketing for some products implies.
Reasonable expectations look like this:
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Most people don't feel something dramatic in week one
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Subjective improvements in energy, sleep, and recovery often emerge over 4–8 weeks of consistent use
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Individual response varies — your starting NAD+ level, your inflammation baseline, your hormonal context, and your delivery method all matter
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NAD+ isn't a silver bullet. It's an input to a system. The system also needs sleep, movement, low chronic inflammation, and managed stress to function
Also: in healthy adults, NAD+ precursors are generally well tolerated, but mild side effects can include nausea, flushing, or headache. Always work with a provider, especially if you have any underlying conditions or are on other medications.
7 Signs Your NAD+ May Be Low (And When to Take It Seriously)
There's no perfect at-home test for NAD+ levels — but here are the patterns that show up most consistently in patients we see:
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Persistent fatigue that doesn't respond to caffeine, sleep, or rest days
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Brain fog that hits at the same time of day, every day (often 2–4pm)
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Workout recovery that takes noticeably longer than it used to
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Skin changes — duller, drier, slower healing
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Sleep quality that has dropped without an obvious cause
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Mood that feels muted or "flat" without acute stressors
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Weight management that has gotten harder despite stable habits
If 3 or more of these have been showing up for you for 8+ weeks, it's worth a conversation.
How Fitish Approaches NAD+ (the Sporty, Real Version)
Quick brand moment, then back to the science.
At Fitish, we treat NAD+ the way we treat every program we offer: as one input to a real, lived-in body — not a magic pill. Our providers personalize protocols based on your symptoms, your other treatments (HRT, GLP-1, peptides), and your actual energy patterns. Not a one-size template.
We offer NAD+ in multiple delivery formats because the right one for you depends on your goals, your absorption, and your routine. (We covered the differences between nasal spray, oral, and injectable in last week's post — check that one out if you're trying to figure out which to start with.)
That's the playbook. We're here to help you run it.
FAQ — The Questions Patients Actually Ask
Is NAD+ the same as NMN or NR?
Not exactly. NAD+ is the molecule your cells actually use. NMN (nicotinamide mononucleotide) and NR (nicotinamide riboside) are precursors — building blocks your body converts into NAD+. Some products deliver NAD+ directly (IV, injectable, certain nasal sprays); others deliver the precursors and let your body build NAD+ from them.
How long until I feel something?
Most patients describe subtle improvements in energy or sleep within 4–6 weeks of consistent use. The dramatic "day 3 transformation" stories you see online are not the norm. Plan for a season, not a week.
Is NAD+ safe?
In healthy adults, NAD+ and its precursors are generally well tolerated at studied doses. Mild side effects can include nausea, flushing, or headache — usually transient. As with anything, individual factors matter. If you have underlying health conditions, are pregnant or breastfeeding, or are on prescription medications, work with a provider before starting.
Can I take NAD+ with HRT or peptides?
Generally yes — and many of our patients do. NAD+ pairs well with peptide therapy and HRT because they target different mechanisms (cellular energy, growth/repair signaling, hormonal regulation respectively). A provider can help you sequence and dose so they work together rather than competing.
Will NAD+ help me lose weight?
It's not a weight-loss drug. But by improving cellular energy and supporting metabolic function, NAD+ may help indirectly — many patients on GLP-1s report better tolerance and recovery when NAD+ is part of the protocol. The weight changes come from the GLP-1; the energy and resilience benefits come from the NAD+.
How much does NAD+ cost at Fitish?
Our NAD+ programs start at $149/mo for our nasal spray and $219/mo for the higher-dose protocol, with subscription pricing for 3- and 6-month commitments that brings the cost down further. Pricing is transparent — no hidden fees, and dose adjustments are included.
The Bottom Line
NAD+ decline isn't a marketing story. It's a measurable biological reality with peer-reviewed research behind it. By midlife, most adults are running on roughly half the NAD+ they had in their 20s. For women, the perimenopause overlap makes the experience even more pronounced.
The good news: you're not imagining the change in how your body responds to inputs. The other good news: there's a real conversation to be had with a provider who knows what to look for.
If this post made anything click — if you've been asking the wrong questions or getting the wrong answers — that's the place to start.
READY TO LEVEL UP?
Research + References
All claims in this post are anchored to peer-reviewed research from the National Institutes of Health (NIH/PubMed) and major academic journals. We don't cite competitors or commercial-interest sources. Below are the primary references:
• Why NAD+ Declines During Aging: It's Destroyed (PubMed/PMC, 2016)
• Age-related NAD+ decline (PubMed, 2020)
• NAD+ deficiency in age-related mitochondrial dysfunction (PubMed, 2014)
• Dietary Supplementation With NAD+-Boosting Compounds (PubMed/PMC, 2023)
• Impact of NAD+ metabolism on ovarian aging (PubMed/PMC, 2023)