What is an NAD? NAD stands for nicotinamide adenine dinucleotide, a vital coenzyme present in every living cell in the human body. This essential molecule exists in two forms—NAD+ (oxidised) and NADH (reduced)—and plays crucial roles in energy production, DNA repair, and cellular metabolism. As an electron carrier, NAD facilitates hundreds of biochemical reactions that convert nutrients into usable energy. Whilst NAD levels naturally decline with age, most healthy individuals maintain adequate levels through a balanced diet containing niacin (vitamin B3) and tryptophan. Understanding NAD has become increasingly important in metabolic medicine and ageing research, though routine NAD testing is not part of standard NHS practice.

What Does NAD Stand For in Medical Terms?

Note: In UK medical records and test reports, 'NAD' commonly means 'no abnormality detected' (e.g., 'Chest X-ray: NAD'). This article discusses a different NAD—a biological molecule.

NAD stands for nicotinamide adenine dinucleotide, a coenzyme found in every living cell throughout the human body. This essential molecule exists in two forms: NAD+ (the oxidised form) and NADH (the reduced form). Both forms play crucial roles in cellular metabolism, though NAD+ has received particular attention in recent years for its involvement in energy production and cellular repair mechanisms.

As a coenzyme, NAD works alongside enzymes to facilitate hundreds of metabolic reactions. It acts as an electron carrier, shuttling electrons between molecules during cellular respiration—the process by which cells convert nutrients into usable energy in the form of adenosine triphosphate (ATP). Without adequate NAD levels, these fundamental biochemical processes cannot function efficiently.

The discovery of NAD dates back to the early 20th century, when scientists first identified its role in fermentation. Since then, research has revealed its involvement in numerous biological processes beyond energy metabolism, including DNA repair, gene expression, and cellular signalling. Understanding NAD has become increasingly important in fields ranging from ageing research to metabolic medicine.

NAD is synthesised in the body through several pathways, primarily from dietary sources including niacin (vitamin B3) and tryptophan (an amino acid). The body's ability to maintain optimal NAD levels depends on adequate intake of these nutrients, efficient synthesis pathways, and the balance between NAD production and consumption by various cellular processes. For most healthy individuals, a balanced diet provides sufficient precursors for NAD synthesis.

The Role of NAD in Your Body

NAD performs multiple critical functions that maintain cellular health and overall physiological wellbeing. Its primary role involves energy metabolism, where it participates in glycolysis, the citric acid cycle (Krebs cycle), and oxidative phosphorylation. During these processes, NAD+ accepts electrons from nutrients such as glucose and fatty acids, becoming reduced to NADH. This NADH then delivers electrons to the mitochondrial electron transport chain, ultimately generating ATP—the energy currency that powers virtually all cellular activities.

Beyond energy production, NAD serves as a substrate for several important enzyme families. Sirtuins, a group of seven proteins (SIRT1-7), require NAD+ to function and regulate processes including DNA repair, inflammation, circadian rhythms, and metabolic homeostasis. These enzymes have been implicated in longevity and healthy ageing, though research in humans remains ongoing. Similarly, poly(ADP-ribose) polymerases (PARPs) consume NAD+ whilst repairing damaged DNA, maintaining genomic stability.

NAD also supports the immune system and inflammatory responses. It influences the activity of immune cells and helps regulate inflammatory signalling pathways, though much of this evidence comes from laboratory and early clinical studies. Additionally, NAD participates in redox balance—the equilibrium between oxidation and reduction reactions that protects cells from oxidative stress and damage from free radicals.

The NAD+/NADH ratio within specific cellular compartments can serve as an indicator of metabolic state. A higher ratio generally suggests efficient energy production and cellular function, whilst a lower ratio may indicate metabolic stress or dysfunction. This ratio naturally declines with age, which has prompted investigation into whether maintaining NAD+ levels might support healthy ageing, though definitive clinical evidence in humans remains limited. It's important to note that NAD levels are not measured in routine NHS clinical practice.

Should You Consider NAD Therapy?

NAD therapy typically refers to interventions aimed at increasing NAD+ levels, either through supplementation with precursors or, less commonly, intravenous NAD+ infusions. Whilst research into NAD supplementation has grown substantially, it is important to note that there is currently no official NICE guidance specifically recommending NAD therapy for any medical condition, and much of the evidence base remains preliminary.

Oral supplements containing nicotinamide riboside (NR) are available as food supplements in the UK. NR is an authorised novel food in Great Britain with specific maximum daily intake limits and is intended for adults only (not recommended during pregnancy or breastfeeding unless advised by a healthcare professional). Some human studies show NR can increase circulating NAD+ levels, but the clinical significance of these increases requires further investigation through rigorous clinical trials.

Nicotinamide mononucleotide (NMN) is not currently authorised as a novel food in Great Britain and should not be sold as a food supplement in the UK. Consumers should be cautious about unregulated NMN products.

Intravenous NAD+ therapy, sometimes offered at private clinics, involves direct infusion of NAD+ into the bloodstream. Proponents claim benefits for fatigue, cognitive function, and various other conditions, but robust clinical evidence supporting these applications is lacking. There are no UK-licensed NAD+ medicines; IV NAD+ promoted for therapeutic effects would generally be considered an unlicensed medicinal product within the MHRA's regulatory remit and should not be used outside research or specialist oversight.

Before considering NAD therapy, individuals should:

• Consult their GP or healthcare provider to discuss whether supplementation is appropriate for their circumstances

• Ensure adequate dietary intake of niacin (vitamin B3) through foods such as meat, fish, nuts, and fortified cereals

• Consider that a balanced diet typically provides sufficient NAD precursors for healthy individuals

• Be aware that supplements are not subject to the same regulatory standards as medicines

• Recognise that long-term safety data for high-dose NAD precursor supplementation remains limited

• Check that any clinic offering IV infusions is appropriately regulated (e.g., CQC-registered)

For most people, maintaining NAD levels through a nutritious diet, regular physical activity, and healthy lifestyle habits represents the most evidence-based approach.

If you experience suspected side effects from any medicine or supplement, report them via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk).

NAD Deficiency: Causes and Symptoms

True NAD deficiency is relatively uncommon in developed countries but can occur through several mechanisms. The most recognised cause is severe niacin (vitamin B3) deficiency, which leads to pellagra—a condition characterised by the classic triad of dermatitis, diarrhoea, and dementia. Pellagra is now rare in the UK due to adequate dietary niacin intake and food fortification, but may occasionally occur in individuals with severe malnutrition, chronic alcoholism, or certain malabsorptive disorders such as Crohn's disease or Hartnup disease (a rare genetic condition affecting tryptophan absorption).

Subclinical reductions in NAD levels, rather than frank deficiency, may occur with:

• Advancing age—NAD+ levels naturally decline with ageing, though the clinical implications remain under investigation

• Chronic diseases including diabetes, obesity, and cardiovascular disease, which may increase NAD+ consumption

• Excessive alcohol consumption, which disrupts NAD metabolism

• Certain medications that interfere with niacin metabolism (e.g., isoniazid used for tuberculosis treatment)

• Carcinoid syndrome, which can divert tryptophan metabolism away from NAD synthesis

• Genetic disorders affecting NAD synthesis pathways (extremely rare)

Symptoms of significant NAD deficiency typically reflect impaired energy metabolism and cellular function. In pellagra, patients present with:

• Photosensitive dermatitis, particularly on sun-exposed areas

• Gastrointestinal symptoms including diarrhoea, nausea, and glossitis (inflamed tongue)

• Neurological manifestations such as confusion, memory impairment, and in severe cases, encephalopathy

Milder reductions in NAD may theoretically contribute to fatigue, reduced exercise tolerance, and metabolic dysfunction, though there is no official link established between subtle NAD reductions and specific symptom patterns. These non-specific symptoms have numerous potential causes and require proper medical evaluation.

It's important to note that there is no routine NHS blood test for 'NAD levels'. Pellagra is primarily a clinical diagnosis based on symptoms, dietary history, and response to treatment. Treatment typically involves nicotinamide supplementation under medical supervision.

If you experience persistent fatigue, skin changes, gastrointestinal symptoms, or cognitive difficulties, contact your GP for appropriate assessment rather than self-diagnosing NAD deficiency. Seek urgent medical attention for confusion, severe diarrhoea/dehydration, or extensive photosensitive rash. Your doctor can arrange relevant investigations, including nutritional assessment and blood tests, to identify the underlying cause and recommend evidence-based treatment.

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