Aging cells. Old human fibroblasts showing their mitochondria in large branched networks (red), their nuclear DNA (blue) and sites of DNA damage (green). (Image: Glyn Nelson/Flickr)

Whenever I see my 10-year-old daughter brimming over with so much energy that she jumps up in the middle of supper to run around the table, I think to myself, "those young mitochondria."

Mitochondria are our cells' energy dynamos. Descended from bacteria that colonized other cells about 2 billion years, they get flaky as we age. A prominent theory of aging holds that decaying of mitochondria is a key driver of aging. While it's not clear why our mitochondria fade as we age, evidence suggests that it leads to everything from heart failure to neurodegeneration, as well as the complete absence of zipping around the supper table.

Recent research suggests it may be possible to reverse mitochondrial decay with dietary supplements that increase cellular levels of a molecule called NAD (nicotinamide adenine dinucleotide). But caution is due: While there's promising test-tube data and animal research regarding NAD boosters, no human clinical results on them have been published.

Structure of nicotinamide adenine dinucleotide, oxidized (NAD+). (Image: NEUROtiker/Wikimedia)

NAD is a linchpin of energy metabolism, among other roles, and its diminishing level with age has been implicated in mitochondrial deterioration. Supplements containing nicotinamide riboside, or NR, a precursor to NAD that's found in trace amounts in milk, might be able to boost NAD levels. In support of that idea, half a dozen Nobel laureates and other prominent scientists are working with two small companies offering NR supplements.

The NAD story took off toward the end of 2013 with a high-profile paper by Harvard's David Sinclair and colleagues. Sinclair, recall, achieved fame in the mid-2000s for research on yeast and mice that suggested the red wine ingredient resveratrol mimics anti-aging effects of calorie restriction. This time his lab made headlines by reporting that the mitochondria in muscles of elderly mice were restored to a youthful state after just a week of injections with NMN (nicotinamide mononucleotide), a molecule that naturally occurs in cells and, like NR, boosts levels of NAD.

It should be noted, however, that muscle strength was not improved in the NMN-treated mice—the researchers speculated that one week of treatment wasn't enough to do that despite signs that their age-related mitochondrial deterioration was reversed.

NMN isn't available as a consumer product. But Sinclair's report sparked excitement about NR, which was already on the market as a supplement called Niagen. Niagen's maker, ChromaDex, a publicly traded Irvine, Calif., company, sells it to various retailers, which market it under their own brand names. In the wake of Sinclair's paper, Niagen was hailed in the media as a potential blockbuster.

In early February, Elysium Health, a startup cofounded by Sinclair's former mentor, MIT biologist Lenny Guarente, jumped into the NAD game by unveiling another supplement with NR. Dubbed Basis, it's only offered online by the company. Elysium is taking no chances when it comes to scientific credibility. Its website lists a dream team of advising scientists, including five Nobel laureates and other big names such as the Mayo Clinic's Jim Kirkland, a leader in geroscience, and biotech pioneer Lee Hood. I can't remember a startup with more stars in its firmament.

A few days later, ChromaDex reasserted its first-comer status in the NAD game by announcing that it had conducted a clinical trial demonstrating that “a single dose of NR resulted in statistically significant increases” in NAD in humans—the first evidence that supplements could really boost NAD levels in people. Details of the study won't be out until it's reported in a peer-reviewed journal, the company said. (ChromaDex also brandishes Nobel credentials: Roger Kornberg, a Stanford professor who won the Chemistry prize in 2006, chairs its scientific advisory board. He’s the son of Nobel laureate Arthur Kornberg, who, ChromaDex proudly notes, was among the first scientists to study NR some 60 years ago.)

Sirt1 protein, red, circles the cell's chromosomes, blue. (Image: Ana Gomes/Sinclair Lab)

The NAD findings tie into the ongoing story about enzymes called sirtuins, which Guarente, Sinclair and other researchers have implicated as key players in conferring the longevity and health benefits of calorie restriction. Resveratrol, the wine ingredient, is thought to rev up one of the sirtuins, SIRT1, which appears to help protect mice on high doses of resveratrol from the ill effects of high-fat diets. A slew of other health benefits have been attributed to SIRT1 activation in hundreds of studies, including several small human trials.

Here's the NAD connection: In 2000, Guarente's lab reported that NAD fuels the activity of sirtuins, including SIRT1—the more NAD there is in cells, the more SIRT1 does beneficial things. One of those things is to induce formation of new mitochondria. NAD can also activate another sirtuin, SIRT3, which is thought to keep mitochondria running smoothly.

The Sinclair group's NAD paper drew attention partly because it showed a novel way that NAD and sirtuins work together. The researchers discovered that cells' nuclei send signals to mitochondria that are needed to maintain their normal operation. SIRT1 helps insure the signals get through. When NAD levels drop, as they do with aging, SIRT1 activity falls off, which in turn makes the crucial signals fade, leading to mitochondrial dysfunction and all the ill effects that go with it.

NAD boosters might work synergistically with supplements like resveratrol to help reinvigorate mitochondria and ward off diseases of aging. Elysium is banking on this potential synergy—its NR-containing supplement includes a resveratrol-like substance called pterostilbene (pronounced tero-STILL-bean), which is found in blueberries and grapes.

Why pterostilbene instead of resveratrol?

While resveratrol has hogged the anti-aging spotlight over the past decade, unsung researchers in places like Oxford, Miss., have quietly shown that pterostilbene is a kind of extra-potent version of resveratrol. The pterostilbene molecule is nearly identical to resveratrol's except for a couple of differences that make it more "bioavailable" (animal studies indicate that about four times as much ingested pterostilbene gets into the bloodstream as resveratrol). Test-tube and rodent studies also suggest that pterostilbene is more potent than resveratrol when it comes to improving brain function, warding off various kinds of cancer and preventing heart disease.

Elysium isn't the only pterostilbene vendor. In fact, ChromaDex also offers pterostilbene for supplements separately from Niagen.

How excited should we be about all this? If I were a middle-aged mouse, I'd be ready to spend some of the nickels and dimes I'd dragged off the sidewalk to try NR supplements. Even before Sinclair's paper, researchers had shown in 2012 that when given doses of NR, mice on high-fat diets gained 60 percent less weight than they did on the same diets without NR. Further, none of the mice on NR showed signs of diabetes, and their energy levels improved. The scientists reportedly characterized NR's effects on metabolism as "nothing short of astonishing."

But the paucity of human data gives me pause. Nobel laureates notwithstanding, I plan to wait until more is known before jumping up from the supper table to run out for some NR. Besides, it probably won’t be long before more data come out given the growing buzz about NAD.