The Science of NAD+: Why Winter Is the Worst Season for Your NAD+ Levels

If you've been paying attention to the longevity and wellness space lately, three letters keep coming up: NAD+. Scientists, biohackers, and researchers are increasingly focused on this molecule and for good reason. NAD+ sits at the very heart of how our cells make energy, repair themselves, and age. Understanding it may be one of the most important things you can do for your long-term health.

What Is NAD+ and Why Does It Matter?

Nicotinamide adenine dinucleotide (NAD+) is a coenzyme found in every living cell. It plays a central role in cellular energy metabolism specifically in the mitochondrial process that converts the food we eat into ATP, the usable energy currency of the cell.

But NAD+ does more than just power your cells. It also activates a family of proteins called sirtuins (often called the "longevity genes"), which regulate cellular repair, inflammation, and stress responses. It also fuels PARP enzymes, which are responsible for DNA repair.

The critical problem? NAD+ levels decline with age often by as much as 50% between young adulthood and middle age, according to research published in Cell Metabolism (Yoshino et al., 2018). This decline has been linked in preclinical studies to reduced mitochondrial function, slower cellular repair, and many of the hallmarks associated with biological aging.

The NAD+ Decline: What the Science Says

Several key studies have shaped our understanding of NAD+ and aging:

• Verdin (2015) in Science highlighted NAD+ as a critical regulator of metabolism and aging, noting its role in sirtuin activation and mitochondrial homeostasis.

• Rajman, Chwalek & Sinclair (2018) in Cell Metabolism reviewed NAD+ precursors as a strategy to restore cellular NAD+ levels, supporting energy metabolism in aging tissues.

• Imai & Guarente (2014) in Trends in Cell Biology demonstrated that boosting NAD+ in aged mice restored aspects of mitochondrial and muscle function — a landmark paper that energised human research.

The consensus emerging from this body of work is that supporting NAD+ levels through precursors and cofactors may be one of the most promising areas of longevity science.

Why Winter Is the Worst Season for Your NAD+ Levels

Most people expect to feel more tired, sluggish, and run-down during the colder months and simply put it down to the weather or the season. But there is real biology behind why winter Is the worst season for your NAD+ levels.

Reduced Sunlight and NAD+ Consumption

One of the most significant and least discussed winter factors is reduced UV exposure. Sunlight-induced DNA damage in skin cells is a major trigger for PARP enzyme activation, which rapidly consumes NAD+ as part of the DNA repair process. While this sounds counterproductive, the issue in winter is more nuanced: reduced light exposure disrupts circadian rhythm signalling, which in turn affects the expression of NAMPT the rate-limiting enzyme in the primary NAD+ biosynthesis pathway (the salvage pathway).

Research has shown that NAMPT expression follows a circadian pattern, meaning that disrupted sleep-wake cycles from shortened winter daylight can impair the body's ability to produce NAD+ efficiently.

Research reference: Ramsey K.M. et al. (2009). Circadian clock feedback cycle through NAMPT-mediated NAD+ biosynthesis. Science. doi:10.1126/science.1171641

Cold, Stress, and Immune Activation

Winter brings with it a heightened immune burden from seasonal respiratory illnesses to the physiological stress of thermoregulation in the cold. Both immune activation and stress responses are major consumers of NAD+. The immune system relies heavily on NAD+ to fuel the inflammatory response, and PARP enzymes are activated by the DNA damage that accompanies infection and cellular stress. Every time the immune system is called into action, it draws on the body's NAD+ reserves.

For people who are already experiencing age-related NAD+ decline, this added seasonal demand can create a meaningful deficit contributing to the fatigue, brain fog, and reduced resilience many people experience in winter.

Reduced Physical Activity

Winter tends to mean less movement and that matters for NAD+. Exercise is one of the most well-established natural ways to upregulate NAMPT and support NAD+ biosynthesis. Research by Costford et al. (2010) in Diabetes found that NAMPT expression in muscle tissue was positively associated with physical activity levels. When movement drops in winter, so does one of the body's most reliable NAD+-boosting mechanisms.

Dietary Changes in Winter

Winter diets tend to shift toward more comfort foods and less fresh produce meaning lower intake of NAD+ precursor-rich foods like edamame, avocado, mushrooms, and leafy greens. The tryptophan-to-NAD+ conversion pathway (the de novo synthesis pathway) also relies on dietary inputs that may be reduced during this period. Combined with the other seasonal pressures above, the nutritional contribution to NAD+ production can quietly decline.

Why Consistent Supplementation Matters More in Winter

Given the multiple seasonal pressures on NAD+ disrupted circadian rhythms, increased immune demand, reduced exercise, and dietary shifts winter is arguably the most important time of year to maintain consistent NAD+ support through supplementation.

Unlike many wellness habits that can be paused seasonally, the biological argument for NAD+ support is actually stronger in winter precisely because natural replenishment pathways are under greater strain. Maintaining NAD+ levels isn't just about optimising longevity in the abstract it's about giving your cells the energy currency they need to handle the real demands of the season: immune challenges, reduced light, and metabolic stress.

This is also why a year-round, consistent supplementation approach rather than sporadic or summer-only use better reflects the underlying science. NAD+ decline is a 365-day process accelerated by aging and compounded by seasonal stressors. Consistent support with direct NAD+ precursors like NMN and NR, alongside complementary compounds that protect and amplify NAD+ function, is how you keep cellular energy from bottoming out when your body needs it most.

How to Support NAD+ Levels: The Role of Longevity Supplements

This is where the world of longevity supplements becomes fascinating. Several compounds have been studied for their ability to directly or indirectly support NAD+ biosynthesis and activity.

1. NMN (Nicotinamide Mononucleotide)

NMN is arguably the most direct NAD+ precursor available. Once absorbed, NMN is converted into NAD+ through the salvage biosynthesis pathway. In a landmark human clinical trial published in NPI Aging (Katayoshi et al., 2023), NMN supplementation was shown to raise blood NAD+ levels in healthy adults.

Animal studies, particularly those from David Sinclair's lab at Harvard, have shown that NMN supplementation improved mitochondrial function and physical endurance in aged mice.

Research reference: Yoshino M. et al. (2021). Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women. Science. doi:10.1126/science.abe9985

2. NR (Nicotinamide Riboside)

NR is another direct NAD+ precursor and is converted to NMN before becoming NAD+. It's one of the most studied NAD+ boosters in human trials. A randomised controlled trial by Trammell et al. (2016) in Nature Communications confirmed that oral NR supplementation safely and significantly increased NAD+ metabolite levels in healthy adults.

Research reference: Trammell S.A. et al. (2016). Nicotinamide riboside is uniquely and orally bioavailable in healthy humans. Nature Communications. doi:10.1038/ncomms12948

3. Resveratrol

Resveratrol, the polyphenol found in red grape skins, doesn't raise NAD+ directly but it activates SIRT1, the primary sirtuin that NAD+ powers. Think of NAD+ as the fuel and resveratrol as the accelerator. Research from Sinclair et al. (2003) in Nature famously showed that resveratrol activates Sir2 (the yeast equivalent of SIRT1), extending lifespan in model organisms.

In human biology, resveratrol's sirtuin-activating effects mean it may amplify the benefits of NAD+ when levels are supported. Studies suggest it also supports mitochondrial biogenesis the process of creating new mitochondria.

Research reference: Howitz K.T. et al. (2003). Small molecule activators of sirtuins extend Saccharomyces cerevisiae lifespan. Nature. doi:10.1038/nature01965

4. Pterostilbene

Pterostilbene is structurally similar to resveratrol but has superior bioavailability it's absorbed more readily and stays in circulation longer. Like resveratrol, it activates SIRT1 and SIRT3, supporting NAD+-dependent cellular pathways.

Research published in Advances in Nutrition (McCormack & McFadden, 2013) highlighted pterostilbene's potent antioxidant and SIRT-activating properties.

5. Spermidine

Spermidine is a naturally occurring polyamine found in wheat germ, aged cheese, and mushrooms. Its relevance to cellular energy and longevity research centres on its ability to induce autophagy the cellular "self-cleaning" process by which damaged components are recycled. Autophagy is closely linked to mitochondrial quality control, which in turn affects NAD+ metabolism.

Research from Eisenberg et al. (2016) in Nature Medicine demonstrated that spermidine supplementation extended lifespan in model organisms and improved cardiac function in ageing mice by inducing autophagy.

Research reference: Eisenberg T. et al. (2016). Cardioprotection and lifespan extension by the natural polyamine spermidine. Nature Medicine. doi:10.1038/nm.4222

6. Fisetin

Fisetin is a flavonoid found in strawberries, apples, and onions that has attracted significant attention as a senolytic a compound that may help clear senescent ("zombie") cells that accumulate with age and impair tissue function. These senescent cells are associated with chronic low-grade inflammation and reduced mitochondrial efficiency.

Research from Yousefzadeh et al. (2018) in EBioMedicine found that fisetin was among the most potent senolytics tested, reducing senescent cell burden in multiple tissues of aged mice and extending median and maximum lifespan.

Research reference: Yousefzadeh M.J. et al. (2018). Fisetin is a senotherapeutic that extends health and lifespan. EBioMedicine. doi:10.1016/j.ebiom.2018.09.015

7. Quercetin

Like fisetin, quercetin is classified as a senolytic and works synergistically when combined with other compounds. It also has anti-inflammatory and antioxidant properties that support the cellular environment in which NAD+-dependent enzymes operate. Quercetin has been explored in the Mayo Clinic's dasatinib + quercetin (D+Q) senolytic studies, representing some of the first human clinical senolytic research.

Research reference: Xu M. et al. (2018). Senolytics improve physical function and increase lifespan in old age. Nature Medicine. doi:10.1038/s41591-018-0092-9

8. Glutathione

Glutathione is the body's master antioxidant and plays a critical supporting role in cellular energy. Mitochondria generate reactive oxygen species (ROS) as a byproduct of energy production glutathione helps neutralise these, protecting the very machinery that produces energy. As NAD+ supports mitochondrial respiration, glutathione helps ensure that process is sustainable by managing oxidative stress.

Research reference: Pizzorno J. (2014). Glutathione! Integrative Medicine: A Clinician's Journal.

9. Urolithin A

Urolithin A is a postbiotic compound produced when gut bacteria metabolise ellagitannins from pomegranates and other foods. It is notable for activating mitophagy the selective removal of damaged mitochondria which is essential for maintaining a healthy, efficient mitochondrial pool.

A landmark human clinical trial published in Nature Metabolism (Andreux et al., 2019) showed that Urolithin A supplementation increased mitochondrial gene expression and muscle endurance in older adults making it one of the very few longevity compounds with direct human evidence for mitochondrial support.

Research reference: Andreux P.A. et al. (2019). The mitophagy activator urolithin A is safe and induces a molecular signature of improved mitochondrial and cellular health in humans. Nature Metabolism. doi:10.1038/s42255-019-0073-4

10. Ca-AKG (Calcium Alpha-Ketoglutarate)

Alpha-ketoglutarate (AKG) is a key metabolite in the Krebs cycle the core of mitochondrial energy metabolism. As a calcium salt, Ca-AKG is the bioavailable supplemental form. Beyond energy metabolism, AKG serves as a co-substrate for TET enzymes involved in epigenetic regulation, an area closely linked to biological aging.

Research from Shahmirzadi et al. (2020) in Cell Metabolism showed that AKG supplementation extended healthspan in mice and was associated with reduced markers of epigenetic aging.

Research reference: Shahmirzadi A.A. et al. (2020). Alpha-ketoglutarate, an endogenous metabolite, extends lifespan and compresses morbidity in aging mice. Cell Metabolism. doi:10.1016/j.cmet.2020.08.004

Ageless X7: A Comprehensive Longevity Formula

For those looking to combine the power of multiple longevity compounds in one formulation, an all-in-one stack containing seven key anti-aging ingredients offers a convenient and synergistic approach. Rather than managing numerous individual supplements, a well-designed multi-compound formula can ensure these ingredients work together supporting NAD+ biosynthesis, sirtuin activation, autophagy, senolytic activity, and mitochondrial health simultaneously.

The concept of compound synergy in longevity science is well-supported: for example, NMN raises NAD+ levels while resveratrol amplifies sirtuin activity, and fisetin + quercetin target senescent cells while spermidine clears damaged cellular components. Together, they address aging from multiple biological angles.

Putting It All Together: A Systems View of Cellular Energy and Aging

Here's a simplified view of how these compounds interact with NAD+ and cellular energy:

Supplement	Primary Mechanism	Link to NAD+
NMN	Direct NAD+ precursor	Directly raises NAD+
NR	Direct NAD+ precursor	Directly raises NAD+
Resveratrol	SIRT1 activator	Amplifies NAD+-driven sirtuin activity
Pterostilbene	SIRT1/SIRT3 activator	Amplifies NAD+-driven sirtuin activity
Spermidine	Autophagy inducer	Supports mitochondrial quality
Fisetin	Senolytic	Clears cells that impair energy metabolism
Quercetin	Senolytic + antioxidant	Reduces oxidative burden on mitochondria
Glutathione	Master antioxidant	Protects mitochondria from oxidative stress
Urolithin A	Mitophagy activator	Renews the mitochondrial pool
Ca-AKG	Krebs cycle metabolite	Directly supports mitochondrial respiration

The Bottom Line

The science of NAD+ and cellular energy is one of the most exciting areas of longevity research today. While much of the most dramatic evidence comes from animal models and early human trials, the mechanistic rationale is compelling and the pace of human research is accelerating rapidly.

Supporting NAD+ levels, activating sirtuins, clearing senescent cells, and maintaining mitochondrial quality are not isolated interventions they are interconnected pillars of cellular health. Longevity supplements like NMN, NR, resveratrol, pterostilbene, spermidine, fisetin, quercetin, glutathione, urolithin A, and Ca-AKG each address one or more of these pillars.

As always, supplements work best as part of a broader approach to health that includes good nutrition, regular physical activity, quality sleep, and stress management. If you're considering adding any of these compounds to your routine, it's worth discussing with a healthcare professional familiar with longevity research.

The information in this article is intended for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before beginning any new supplement regimen.

References:

1. Yoshino J. et al. (2018). NAD+ Intermediates. Cell Metabolism.

2. Verdin E. (2015). NAD+ in aging, metabolism, and neurodegeneration. Science.

3. Rajman L., Chwalek K., Sinclair D.A. (2018). Therapeutic Potential of NAD-Boosting Molecules. Cell Metabolism.

4. Trammell S.A. et al. (2016). Nicotinamide riboside is uniquely and orally bioavailable in healthy humans. Nature Communications.

5. Howitz K.T. et al. (2003). Small molecule activators of sirtuins extend Saccharomyces cerevisiae lifespan. Nature.

6. Eisenberg T. et al. (2016). Cardioprotection and lifespan extension by the natural polyamine spermidine. Nature Medicine.

7. Yousefzadeh M.J. et al. (2018). Fisetin is a senotherapeutic that extends health and lifespan. EBioMedicine.

8. Xu M. et al. (2018). Senolytics improve physical function and increase lifespan in old age. Nature Medicine.

9. Andreux P.A. et al. (2019). The mitophagy activator urolithin A is safe and induces a molecular signature of improved mitochondrial and cellular health in humans. Nature Metabolism.

10. Shahmirzadi A.A. et al. (2020). Alpha-ketoglutarate, an endogenous metabolite, extends lifespan and compresses morbidity in aging mice. Cell Metabolism.

11. Ramsey K.M. et al. (2009). Circadian clock feedback cycle through NAMPT-mediated NAD+ biosynthesis. Science.

12. Costford S.R. et al. (2010). Skeletal muscle NAMPT is induced by exercise in humans. American Journal of Physiology — Endocrinology and Metabolism