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Eating your greens could actually make you look younger, a study has found.

A compound found in broccoli, cabbage and avocado has been found to slow the signs of physical ageing .

Now scientists claim the substance, known as nicotinamide mononucleotide or NMN, could keep elderly people "younger" and healthier.

Experiments saw older mice given the compound and found that it slowed their physical ageing and gave them the metabolism of much younger mice.

It reduced typical signs of ageing including in skeletal muscle, liver function, bone density, eye function, insulin sensitivity, immune function, body weight and physical activity levels.

(Image: Getty)

When the compound was given to younger mice, it had little affect on them.

Human health hinges on how well the body manufactures and uses energy, but as we age the cells' ability to produce energy declines.

While scientists are unsure why this happens, they suspect loss of efficiency in the body's energy supply is a key driver of the ageing process.

The study found that NMN can compensate for this loss of energy production.

Professor Dr Shin-ichiro Imai, from Washington University School of Medicine, said: "We have shown a way to slow the physiologic decline that we see in ageing mice.

"This means older mice have metabolism and energy levels resembling that of younger mice.

"Since human cells rely on this same energy production process, we are hopeful this will translate into a method to help people remain healthier as they age."

The next step is to carry out clinical trials on humans in Japan to test the safety of NMN - nicotinamide mononucleotide.

(Image: Getty)

With age, the body loses its capacity to make a key element of energy production called NAD (nicotinamide adenine dinucleotide).

Previous research has shown NAD levels decrease in multiple tissues as mice age and NAD is not effective when given directly to mice.

To boost levels the researchers only had to look one step earlier in the NAD supply chain to NMN.

When NMN is dissolved in drinking water and given to mice, it appears in the bloodstream in less than three minutes and is quickly converted to NAD in multiple tissues.

Mice of varying ages were given NMN water to explore the long-term effects.

(Image: Micheal Worful/SWNS.com)

There was a variety of beneficial effects of NMN supplementation, but these benefits were seen exclusively in older mice.

Co-senior author assistant professor Dr Jun Yoshino said: "When we give NMN to the young mice, they do not become healthier young mice.

"NMN supplementation has no effect in the young mice because they are still making plenty of their own NMN.

"We suspect that the increase in inflammation that happens with ageing reduces the body's ability to make NMN and, by extension, NAD."

In skeletal muscle NMN helped energy metabolism by improving the function of mitochondria, which operate as cellular power plants.

The study also found mice given NMN gained less weight with ageing even as they consumed more food, likely because their boosted metabolism generated more energy for physical activity.

They also had better retina function, as well as increased tear production, which is often lost with ageing.

Older mice had improved insulin sensitivity and this difference remained significant even when they corrected for differences in body weight.

(Image: Getty)

In an earlier study the researchers showed how NAD worked in influencing glucose metabolism and the body's fat tissue.

Mice had a defect in the ability to manufacture NAD only in the body's fat tissue.

And there was no increase in cancer rates.

Prof Imai explained: "Some tumour cells are known to have a higher capability to synthesise NAD, so we were concerned that giving NMN might increase cancer incidence.

"But we have not seen any differences in cancer rates between the groups."

The study was published in the journal Cell Metabolism.