Ageing is associated with numerous clinical problems, such as arthritis, cardiovascular disease, hypertension and Alzheimer’s disease—to name a few. Another issue that occurs with aging is that there are dramatic changes in body composition, with an increase in body fat and a decrease in the amount of muscle.
Within the research and clinical world, this loss in the amount of muscle is known as sarcopenia, from the Greek words for flesh (sarx) and loss (penia). Sarcopenia occurs even in healthy active older people and is characterised by a loss of muscle mass at a rate of approximately 0.5-2.0 percent per year and has an incidence of 13-24 percent in those aged 50-70 years and up to 50 percent in those over 80 years of age. Along with the decrease in muscle mass, older people tend to accumulate excess fat both around and within the muscle.
As one would expect, these changes in body composition can have detrimental consequences for physical performance in the elderly population. Indeed, skeletal muscle is required for activities of everyday life, for example, stepping onto a bus, rising from a chair, putting on a jacket and walking even short distances.
We, therefore, see substantial impairments in muscle strength and the ability to carry out these simple functional tasks, which can reduce older adults’ quality of life and increase the risk of falls and subsequent hospitalisation. There is also a substantial economic cost associated with sarcopenia, with this estimated to be US$18.5 billion in the US in the year 2000. Taken together it is easy to see why methods to treat sarcopenia are of the utmost importance, especially with the increasing age of the world population.
Well-Thought Nutritional Strategies
It is known that resistance exercise can increase muscle mass and function and that this can have positive benefits even in these over 90 years of age. However, while older people do have an adaptive response to resistance exercise, they are unable to respond to the same level as younger people.
This has led to a wealth of research attempting to uncover dietary changes that may be used to further enhance the adaptive abilities of older muscle.
Amino Acids (Leucine)
The rate at which muscle is synthesised is controlled by the balance between muscle building (muscle protein synthesis) and muscle degradation (muscle protein breakdown), ie: muscle can grow through an increase in muscle protein synthesis, a decrease in muscle protein breakdown or a combination of both.
In muscles from older people, it has been shown by researchers that both muscle protein synthesis and breakdown are negatively affected and so both are potential targets for nutritional interventions.
Leucine is an essential branched chain amino acid that has been found to play a crucial role in controlling the rate at which muscle is synthesised, ie: grows. Interestingly, research in young healthy volunteers has shown that leucine can both stimulate muscle protein synthesis and inhibit protein breakdown, changes beneficial to muscle growth.
Some studies have used high leucine meals, instead of supplements. For example, a four ounce serving of lean beef has been found to increase muscle protein synthesis by over 50 percent in the five hours following the meal.
In older adults, however, the response of muscle to leucine is diminished, meaning, primarily, that muscle protein synthesis does not increase to the same degree as it does in the young. Importantly though, although the size of the response is reduced, leucine can still have muscle building effects in the elderly, with approximately three g of leucine suggested to be the amount that will maximise this response in a single dose.
Unfortunately, however, there is a dearth of long term studies investigating leucine supplementation in the elderly. This is vital as determining whether these acute changes in muscle protein breakdown/synthesis translate into clinical benefits in muscle function is of obvious importance.
One study carried out in the Netherlands actually found that supplementing older peoples’ diet with 7.5 g of leucine (2.5 g with each meal) had no beneficial effect on muscle mass or strength over a twelve week period. The reasons for the lack of beneficial effects in this study are not clear and further research is clearly required to determine whether leucine can be an effective supplement in the treatment of sarcopenia.
There are a variety of dietary sources of leucine with sources such as soybeans, lentils, peanuts and read meat being relatively high in their content (around 1.5-3 g leucine per 100 g of food). Other dietary sources include dairy foods such as milk and eggs, with a pint of milk having approximately 1.5 g of leucine in it.
STUDIES HAVE FOUND THAT VITAMIN D SUPPLEMENT CAN INCREASE MUSCLE STRENGTH AND REDUCE THE RISK OF FALLS.
It is thought that some of the loss of muscle mass with age can be attributed to an imbalance between anti- and pro-oxidants, in the favour of a pro-oxidant state. Some of the most common antioxidants (for example, vitamin C and E, glutathione, carotenoids, flavonoids and ubiquinones) can improve anti-oxidant defence systems and so have been proposed to be useful in the treatment or prevention of sarcopenia.
Antioxidants can be found in a variety of dietary sources such as vegetables, fruits, nuts and spices. To give more specific examples, these include items such as beans, artichokes, cranberries, oranges, blackberries, pecan nuts and cinnamon to name but a few. However, while there is evidence that antioxidant supplementation can be useful in animal models of ageing, ie: increasing muscle protein synthesis, there is yet no convincing evidence in humans.
Vitamin D can be ingested via dietary sources such as oily fish (salmon and sardines), eggs, and fortified fat spreads and breakfast cereals. It can also be produced in the skin from cholesterol when exposed to sufficient sunlight.
For quite some time, it has been known that being deficient in vitamin D results in muscle weakness, alongside several other clinical problems, such as weakness of the bones. In older individuals, particularly those who reside in nursing homes, levels of vitamin D in the blood tend to be lower than they are in younger individuals.
More recently, it has been found that vitamin D can act directly on skeletal muscle and may increase the rates of protein synthesis. Researchers have therefore begun to investigate whether supplementation with vitamin D can have beneficial effects in sarcopenia within older people, with some promising results.
Taken together, these studies have found that Vitamin D supplementation can increase muscle strength and also reduce the risk of falls in nursing home residents with low vitamin D levels.
Fishing For Omega 3
The omega 3 fatty acids are a type of fat, which have a double bond at the third carbon from the end of the carbon chain, and are commonly found in marine and plant sources. The fatty acids that are likely to be important for sarcopenia are known as EPA and DHA and are commonly found in oily fish, or sold over the counter as dietary supplements.
This fish oil has been found to have beneficial effects in numerous age related conditions such as cardiovascular disease, Alzheimer’s disease and type 2 diabetes. In recent years, there has also been considerable interest in the potential for fish oil to have a role in determine muscle size and function in old age.
In a large scale study carried out in England called the Hertfordshire study, a detailed dietary analysis was carried out and components of the diet related to grip strength. The results of this study found that there was a very strong relationship between the number of portions of oily fish (for example, salmon, sardines, herring, mackerel, tuna, etc) eaten in week and grip strength, with those eating over three oily fish portions a week having the highest grip strength.
These findings were of great interest to researchers and this has led to a number of studies which have supplemented older people with fish oil and investigated various aspects of sarcopenia.
Researchers in the US have shown that supplementing the diet with four g per day fish oil for an eight week period can increase muscle protein synthesis in response to a single dose of high levels of amino acids and insulin, making the older muscle respond more like younger muscle.
As with other supplements, it remains important to investigate the long term effects of fish oil supplementation in the older population. This has led researchers in Aberdeen, Scotland (with a similar investigation in Brazil), to determine whether fish oil can improve the response of older people to resistance exercise.
Within the Aberdeen study, older people were supplemented with four g per day fish oil, or placebo, for 12 weeks, during which time, they also performed resistance exercise on two sessions per week.
The results of this study found that whilst the placebo group were able to increase their muscle strength and functional abilities in response to the exercise training, the responses in the fish oil group were almost twice as large. It may be possible, therefore, through increasing the consumption of fish oil or oily fish to make older muscles adapt more like younger muscles.
Taken together, these studies have shown that fish oil, or oily fish consumption, may be useful in preventing or treating the age related loss of muscle mass known as sarcopenia. Alongside the many other benefits of fish consumption, in other diseases, it could well be recommended that consuming four portions of oily fish a week or taking fish oil supplements is a good thing!
[This article originally appeared in the January 2013 issue of APFI.]