NAD+ vs NADH: One Molecule, Two States

Key points

• NAD+ and NADH are the same molecule, nicotinamide adenine dinucleotide, in two states.
• NAD+ is the form that can accept electrons. NADH is the form that is carrying them.
• Inside cells the two forms turn into each other in a loop, which is part of how cells handle energy from food.
• A role inside a cell is biology. It is not evidence of what any supplement does.

What is NADH? NADH is nicotinamide adenine dinucleotide in its reduced form: the form that is carrying electrons. NAD+ is the same molecule in its oxidized form, ready to accept them. So NAD+ and NADH are not two different substances. They are one molecule in two states, and cells switch between them all the time. This guide explains the names, the loop and where it runs.

The short answer: one molecule, two states

NAD+ is short for nicotinamide adenine dinucleotide. It is a molecule found in living cells, where it takes part in energy metabolism as an electron carrier: it accepts electrons in one reaction and passes them on in another.

Inside a cell, NAD+ works as a shuttle. It picks up electrons in one reaction and becomes NADH. It hands them on in another and becomes NAD+ again. That loop is part of how cells handle energy from food.

What the "+" and the "H" stand for

The two names describe the same core molecule with a small difference. The "+" is part of the name of the oxidized form: the form that is ready to accept electrons.

The "H" stands for hydrogen. When NAD+ accepts electrons, it takes them as a hydride: a hydrogen carrying two electrons. With that hydride attached, the molecule is written NADH. A review in Nature Reviews Molecular Cell Biology describes NAD+ in exactly these terms, as a molecule that accepts a hydride ion to form its reduced version, NADH.

Oxidized and reduced, without the jargon

Chemists use two words for this. A molecule that gains electrons is reduced. A molecule that loses them is oxidized.

• NADH is the reduced form: it is carrying electrons.
• NAD+ is the oxidized form: it is ready to accept them.

The words sound odd at first, because "reduced" here means "gained electrons", not "made smaller". Once that is clear, the pair is easy to follow: one molecule, flipping between a loaded state and an empty one.

Where the loop runs inside a cell

NAD+ is not in one place in a cell. A review in Nature Reviews Molecular Cell Biology describes its main pools as the cytoplasm (the fluid that fills the cell), the mitochondria and the nucleus, and notes that these pools are regulated independently of each other.

From food molecules to the electron transport chain

When a cell breaks down molecules that came from food, several steps hand electrons to NAD+, which becomes NADH.

• Glycolysis, the first stage of breaking down glucose, runs in the cytoplasm and produces NADH.
• The citric acid cycle, also called the TCA cycle, runs inside the mitochondria and produces more NADH.

Inside the mitochondria, NADH passes its electrons to Complex I, the first stage of the electron transport chain. Handing them over turns NADH back into NAD+, ready for the next round. The chain itself is a series of four protein complexes that pass electrons along, a process that leads to the making of ATP.

One detail surprises people. NADH made in the cytoplasm does not cross into the mitochondria itself. Shuttle systems in the mitochondrial membrane carry its electrons across instead, according to the same Cell Metabolism review.

NADP+ and NADPH: close relatives with a different job

Cells can add a phosphate group to NAD+ to make NADP+. The extra "P" in the name stands for that phosphate. NADP+ also accepts electrons, and in its loaded form it is written NADPH.

The two pairs tend to do different work. According to the NIH Office of Dietary Supplements, NAD is mainly involved in reactions that break molecules down, while NADP mainly takes part in reactions that build molecules up, such as fatty acids and cholesterol. So NADH and NADPH look almost identical on paper, but they are not interchangeable names.

Why both names appear on supplement shelves

You will see supplements sold under both names: some name NAD+ on the label, others NADH. The name tells you which form the label refers to. Each ingredient raises its own evidence question, and we do not compare products that name one form against products that name the other.

Role is not the same as result

What a molecule does inside a cell is biology. What a supplement does for the person taking it is a separate question, and it needs its own evidence. We explain the first so you know what the word on the label means. We make no claim about the second.

Key terms at a glance

To see where cells get the building blocks to make NAD+ in the first place, read vitamin B3 foods and NAD+. Our Science page sets out the basics in one place.

Frequently asked questions

Is NADH the same as NAD+?

It is the same molecule in a different state. NAD+ is the oxidized form, ready to accept electrons. NADH is the reduced form, carrying them. Cells convert one into the other constantly.

What does the H in NADH stand for?

Hydrogen. NAD+ accepts electrons as a hydride, a hydrogen carrying two electrons, and the result is written NADH.

What is the difference between NADH and NADPH?

NADPH has an extra phosphate group. The NADP pair mainly takes part in building reactions, such as making fatty acids, while the NAD pair is mainly involved in breaking molecules down.

Pure Limitless sells one product: NAD+ Sublingual Drops, a food supplement with 3000mg of NAD+ in total per 30ml bottle.

Sources

• Nature Reviews Molecular Cell Biology: NAD+ metabolism and its roles in cellular processes during ageing
• Cell Press, Cell Metabolism: NAD+ Metabolism and the Control of Energy Homeostasis: A Balancing Act between Mitochondria and the Nucleus
• NIH Office of Dietary Supplements: Niacin: Fact Sheet for Health Professionals
• StatPearls Publishing: Biochemistry, Electron Transport Chain