People first and mice clearly marked
NAD+ studies changed blood tests, not lifespan
Each result tells you who took part, what the test found, and what it left unanswered.
People had small test changes, not proven health gains
Start with the people. Blood tests rose after NR and NMN, two substances cells can turn into NAD+. In one trial, muscle pulled sugar from blood with less insulin. In another, people walked farther. Neither test found whether anyone felt better, avoided illness, or lived longer. Those are small findings. A higher blood number can’t prove a treatment worked. Mouse results are named as mouse results. Every amount tells you what a study used, not what fits you.
Food helps your body replace NAD+
Food gives your body several raw materials for making NAD+. One is tryptophan, part of the protein you eat. Niacin, a vitamin, is another. Your body can also save a used form of niacin and turn it back into NAD+ [5]. NR goes through two changes: first to NMN, then to NAD+ [5].
Cells spend the new NAD+ on energy work, DNA repair, and other tasks [5]. Exercise was linked with more of the protein that turns used niacin back toward NAD+, and trained people had about twice as much of that protein in their muscles. Mice bred to make extra amounts ran about three times as long [7]. In mice, NAD+ also rose and fell over each 24 hours as the body clock changed its supply [6]. Nothing here picks the time for your pill.
NMN raised blood NAD+ and helped on two tests
In the first human NMN trial, middle-aged adults had no stated illness. For 60 days, groups took 300, 600, or 900 milligrams a day. Blood tests showed more NAD+ on day 30 and day 60. People also walked farther. One blood test checked marks on DNA that tend to change with age. That reading didn’t move, which gave no sign that aging slowed. Researchers favored 600 milligrams a day among the amounts tried. No group had a reported safety issue [3].
Another trial enrolled women past menopause who had prediabetes. For 10 weeks, they took 250 milligrams a day. Their muscles needed less insulin to pull sugar from blood. Body weight didn’t change. Neither did their long-term blood sugar [1]. The test didn’t ask whether they noticed a benefit. Neither trial showed that NMN treats a disease.
People had blood changes while mice had broader gains
The people had narrow results. Over 8 weeks, the three NR groups had NAD+ blood rises of 22%, 51%, and 142%. Their amounts were 100/300/1000 milligrams a day. Cholesterol linked with clogged arteries didn’t rise. Another blood reading, which may rise when certain vitamins are low, also stayed level [4]. Other tests found a better muscle response to insulin with 250 milligrams a day of NMN [1]. Walking distance grew after 300–900 milligrams a day [3].
The wider results came from mice. NR helped mice regain hearing after loud noise [12]. Researchers also gave nicotinamide, a vitamin used to make NAD+, to mice at risk for glaucoma. With the highest amount, 93% of their eyes stayed free of glaucoma [14]. A review covered skin tests in people and lab-grown cells. Nicotinamide slowed some skin aging and dark spots [11]. None of this proves NAD+ will guard your hearing, eyes, or skin.
Old mice improved when one NAD+-breaking protein was blocked
This finding came from mice. Mice without the NAD+-breaking protein kept more NAD+ as they aged. Their cells made more usable energy. Their bodies dealt with sugar and fat better [2]. A sirtuin kept working in the cell parts that make energy.
A second test blocked the same protein in old mice. Their tissue regained NAD+, and their bodies dealt with sugar and fat better [8]. Researchers also tested apigenin, a plant substance. First they used lab-grown cells. Then they gave mice a daily injection of 100 milligrams per kilogram of body weight. The mice ate fatty food. Their NAD+ rose, their blood sugar control improved, and their liver fat fell [10]. A review linked loss of the sirtuin with less energy and less guard against cell damage [9]. These results came from mice, so they can’t tell you that the same treatment would help a person.
No NAD+ study has shown longer life in people
A 2025 review gave a blunt answer. Clear gains for people’s health were scarce. Many kinds of animals lose NAD+ with age, but few human tests found the same change. We also know little about NAD+ in each part of a person’s body [13]. An earlier review called raising NAD+ a possible way to study diseases of age. The review didn’t call the idea proved [5].
Here’s the bottom line. Both pill ingredients lifted the NAD+ blood reading [4][3]. Studies haven’t shown that people stayed well or lived longer because of the pills [13]. Much of the broad aging work used mice. IV use has even less sound work with people. The NAD injection and IV NAD+ page explains why. Every cited paper is in the full reference list if you want to check it.