Leucine recommendations too low for older people, study argues
As well as confirming the association between leucine intake and muscle strength and mass in older adults, a team led by researchers from the University of São Paulo has discovered that leucine’s effect plateaus at 7.6-8g per day. This is equivalent to 110-115mg/kg per day - much higher than the WHO’s recommendation of 39mg/kg per day for all adults.
“Besides corroborating with previous reports, our results expand the literature by showing the importance of leucine intake for muscle mass in individuals above 65 years…Altogether, these results reinforce the notion that adequate leucine intake may protect against age-related muscle wasting and its concomitant functional declines,” wrote the researchers in the journal Nutrients.
This study investigated the potential impact of regular daily leucine intake in a cohort of 67 healthy, independent elderly people, using two measures of lower body muscle strength and muscle mass: maximum dynamic muscle strength (1-RM) and quadriceps muscle cross-sectional area (CSA).
Link to muscle mass and strength
The researchers found a moderate, positive association between total daily leucine intake and both 1-RM and quadriceps CSA.
They said these results may be of clinical relevance as lower body muscle groups seem to be more negatively affected by ageing, and higher habitual leucine might serve as a countermeasure.
Biphasic linear regression analysis, adjusted for sex, age and protein intake, revealed a non-linear relationship with total protein intake and a plateau of 7.6-8g per day for daily leucine intake and muscle mass and strength in older adults.
“In conclusion we demonstrated that total daily leucine intake is associated with muscle mass and strength in healthy older individuals and this association remains after controlling for multiple factors, including overall protein intake,” wrote the researchers.
They said that their findings together with those of Szweiga et al and Murphy et al suggest potential cut-offs that can be used to ascertain leucine requirements for older adults targeting muscle mass preservation, as well as serving as guidance for future clinical trials aiming to test these values.
In the Szweiga study, researchers estimated that the leucine requirement for older adults is more than double that of younger people (78 versus 35mg/kg per day). But despite data supporting the potential benefits of higher leucine consumption during ageing, blanket international recommendations remain unaltered.
Overcoming age-related anabolic resistance
The problem, according to the authors of the current study, is that these recommendations do not take into account the effects of age-related anabolic resistance (this is when the body’s ability to synthesise muscle protein in response to stimuli like protein intake and exercise is impaired).
It has been proposed that a higher protein intake may help older people to overcome age-related anabolic resistance, by mitigating losses in muscle mass and strength.
Leucine is also important here, as it is thought to play a pivotal role in stimulating muscle protein synthesis. Leucine deprivation is thought to impair the phosphorylation of the mechanistic target of rapamycin complex 1 - a pivotal pathway linked to anabolic responses and increases in muscle protein synthesis.
A higher protein intake with increased amounts of leucine may, therefore, help to mitigate this issue. This approach has been validated in several studies.
In addition, short term trials (up to two weeks) with leucine supplementation of 3-4g per meal in older adults have shown robust increases in muscle protein synthesis, suggesting that leucine could be used as a strategy for counteracting muscle waste and functional decline during ageing.
The São Paulo researchers recommend randomised controlled trials to test the effectiveness of supplementary leucine to counteract muscle waste in the elderly.
“Daily leucine intake Is positively associated with lower limb skeletal muscle mass and strength in the elderly”
Authors: Lixandrão, M.E.; Longobardi, I.; Leitão, A.E.; Morais, J.V.M.; Swinton, P.A.; Aihara, A.Y.; Goes, P.C.K.; Ugrinowitsch, C.; Candow, D.G.; Gualano, B.; et al.