The fountain of youth does not exist, unfortunately. That being said, your "biological age" could be reversed with just a few lifestyle tweaks.
Our birthday dictates how many years we have been alive, while a person's biological age refers to how old they are on the "inside", taking into account their diet, activity levels and sleep habits.
To better understand how we could become younger – on the inside at least – scientists from the National University of Natural Medicine (NUNM) in Oregon analysed 43 healthy men, aged 50 to 72.
Eighteen of the men embarked on an eight-week programme where they were advised how to maximise their diet, sleep, exercise and relaxation time, while the remaining participants acted as the control group.
Writing in the journal Aging, the NUNM scientists have revealed the 18 men's biological age had reduced by more than three years at the end of the two months.
Many diseases become more common in old age, with cancer, dementia and heart disorders just a few of the conditions that disproportionately affect elderly people.
Delaying ageing by just 2.2 years would reportedly save the global economy $7 trillion (£4.9 trillion) over the next half a century.
"Thus, if interventions can be identified that extend healthspan even modestly, benefits for public health and healthcare economics will be substantial," wrote the scientists.
A person's biological age can be somewhat gauged by their DNA methylation.
Read more: Humans could live to 150
Measured via saliva samples, DNA methylation describes the accumulation of damage and loss of function to an individual's cells.
In 2016, scientists from the National Institutes of Health in Baltimore measured more than 13,000 people's DNA methylation via the so-called Horvath DNAmAge clock.
"Acceleration" of biological ageing was found to be "predictive of mortality", regardless of how long the individual had been alive.
Using the Horvath DNAmAge clock, the NUNM study's 43 men had their biological age measured at the start and end of the experiment.
As part of the eight-week programme, the 18 men ate two cups of leafy green vegetables – like kale, spinach or Swiss chard – a day, as well as the same amount of cruciferous produce, such as cauliflower, broccoli or Brussels sprouts.
They also consumed 6oz (170g) of any animal protein, which had to be "grass-fed, pastured, organic and hormone/antibiotic-free".
Every day, the men also ate a quarter-cup of sunflower and pumpkin seeds, one to two beetroots and two portions of "low-glycaemic fruit", like apples, oranges or grapefruit.
Across the week, the men had three servings of liver and five to 10 eggs.
Carbohydrates were "restricted", with the men also adopting "mild intermittent fasting" – not eating between 7pm and 7am – both of which help to avoid blood sugar spikes.
Their diet was also supplemented with the "fruit and vegetable powder" PhytoGanix and the probiotic UltraFlora Intensive Care.
Throughout the experiment, the men were told to opt for organic produce where possible, with the scientists also stressing the importance of staying hydrated and using healthy oils – like coconut, olive and flaxseed.
When it came to exercise, the men were told to work out for at least half an hour a day, five days a week, "at an intensity of 60%-80% of maximum perceived exertion".
The NHS recommends adults be physically active every day, with experts stressing the more the better and anything is better than nothing.
Those of a working-age are advised to be moderately active for at least 150 minutes a week, which could include brisk walking, gentle cycling or even pushing a lawn mower. If time-pressed, be vigorously active for 75 minutes via jogging, cycling briskly or skipping rope.
To combat stress, the NUNM participants were "prescribed" breathing exercises according to Dr Herbert Benson's "steps to elicit the relaxation response". This involves sitting in a relaxed position with your eyes closed, repeating a word or sound as you breathe for 10 to 20 minutes.
The men also aimed for at least seven hours of sleep a night, towards the lower end of the NHS' six to nine hour recommendation.
The health service recommends people go to bed and rise at the same time every day, even on weekends. Winding down with gentle yoga, a warm bath, soothing music or a relaxing book can help people nod off, while writing a to-do list for the next day may calm a frazzled mind.
Experts also recommend people avoid screens for around an hour before lights-out and make their bedroom "sleep friendly" via a comfortable mattress, pleasant temperature and black-out curtains.
Watch: Beetroot juice promotes healthy ageing
After eight weeks, the NUNM participants on the "diet and lifestyle treatment" had a biological age 3.2 years younger than their counterparts given "no intervention".
The treated men's 5-methyltetrahydrofolate levels were up 15%, with this B vitamin said to support methylation. The amount of fat circulating in their blood was also down 25%.
"These early results appear to be consistent with, and greatly extend, the very few existing studies that have so far examined the potential for biological age reversal," said lead author Dr Kate Fitzgerald.
"It [the study] is unique in its use of a safe, non-pharmaceutical dietary and lifestyle programme, control group and the extent of the age reduction."
The scientists have stressed the study was relatively small, with further research being required.
"We are enrolling participants for a larger study, which we expect will corroborate these findings," said Dr Fitzgerald.
With ageing a driver of many diseases, balancing methylation could help people stay healthier for longer.
"This study provides the first insight into the possibility of using natural alterations to target epigenetic [how a person's behaviour and environment influences their genes] processes and improve our wellbeing, and perhaps even longevity and lifespan," said co-author Dr Moshe Szyf, from McGill University in Montreal.
Dr Fitzgerald agreed, adding: "What is extremely exciting is food and lifestyle practices, including specific nutrients and food compounds known to selectively alter DNA methylation, are able to have such an impact on those DNA methylation patterns we know predict ageing and age-related disease.
"I believe this, together with new possibilities for us all to measure and track our DNA methylation age, will provide significant new opportunities for both scientists and consumers."
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