Diet and Spinal Muscular Atrophy

Summary

Over the last century the average diet in the UK has changed radically. For everyone, getting correct nutrition has never been more complicated. Nutrition is important for good health; being overweight, underweight or having a lack of any part of a normal diet can make any illness worse. In diseases like SMA, malnutrition and a poor diet can contribute to breathing muscle weakness and weakening of the immune system1. The purpose of this short article is to highlight and explain what research has looked into nutrition and SMA over the past three years.

A balanced diet should take into account several different factors: calorie intake (the amount of energy contained in food), fats, protein, carbohydrates, vitamins and minerals (i.e. iron, copper, zinc). Current guidelines on diet for individuals with SMA advise the need for adequate nutrition2. Benefits of achieving the correct diet include improvements in quality of life, muscle function and bone health. The guidelines also advise special attention to be given to nutrition by a trained dietician at every visit to clinic2.

Barriers to getting enough nutrition in SMA

Achieving balanced nutrition for individuals with SMA can be very complicated; changes in how much movement an individual does means that nutritional needs change too.

Individuals with SMA may experience difficulties in lifting food to their mouths, swallowing difficulties, and choking on food. Studies in the past have suggested that swallowing problems are common in SMA, and that at least one problem with swallowing occurs in 36% of individuals affected by some form of SMA3,4. It is equally important to avoid choking due to the risk of breathing in foods (aspirating), and to ensure that individuals get enough nutrition. Nasogastric tubes (a feeding tube up the nose directly into the stomach) and gastrostomy tubes (a tube surgically inserted through the skin directly into the stomach) may be advised for some individuals with SMA. Such tubes are used to avoid swallowing problems and to allow more nutrition to be given; this may even be slowly given overnight.

Individuals with SMA are more likely to experience abdominal discomfort, constipation and reflux. These issues can cause significant distress to individuals and their families, and may be difficult to manage. Because of these symptoms individuals may avoid food, which can lead to further problems. There are several strategies that may be suggested by clinicians to improve these symptoms. These may include a low fat diet, medications, and in some cases surgery.

Calories

A calorie is a measurement of how much energy is found in food. There are no widely accepted guidelines for how many calories should be given to individuals with SMA; this is because the amount of energy needed differs, depending on age and how much activity is being done. Usually dieticians will estimate calorific requirements of individuals with SMA to be 20 to 50% less than other individuals of the same age. It is important that this is checked over a period of time so the plan can be changed according to weight and growth by either a dietician or a doctor.

Poruk and colleagues in 2012 from the United States, reported their findings from a survey of 47 children with SMA Type 1 and their families5. The families involved were asked what food their children were receiving on three separate days. The authors found that, over time, calorific intake was reduced compared to the recommended daily intake of healthy individuals; this may be due to reduced movement and therefore using less energy. Poruk and colleagues also highlighted that calories required over time doesn’t change by a large amount, and that even small increases in calorific intake (as little as 30 calories per day ) can cause significant weight gain. The authors of the study conclude that there are several issues that need to be addressed regarding adequate nutrition in individuals with SMA Type 1; they point out that there isn’t enough information on the use of specialist formulas nor on the best possible fat and calorie content of formulas for children with SMA.

Fat, Protein and Carbohydrates

It is important to get the correct proportion of each of these major components of diet. The dietician may assess that a diet is correct by looking at weight, growth, and levels of certain proteins, salts and minerals found in the blood.

Fatty acids and the way they are used to provide energy (metabolised) in SMA is thought to be different from the way it is metabolised in individuals without SMA. Altering diet in mice with SMA in early life has been shown to have a beneficial effect on the survival of the mice. In particular, a higher proportion of fat in the diet improved survival in the early stages of life in several different animals with different neurological diseases6. It is important to note however, that to date, no studies have looked into the direct effects of increasing the amount of fat individuals with SMA receive and that findings in animal studies do not always correlate with findings in human studies.

Elemental and other specialised formulas are available in the UK; commonly this is an artificial milk with the essential parts of the diet already broken down into its smallest parts. This means that the body doesn’t need to expend energy to break foods down. To date, there has been no trial looking at the effects or potential benefits of this type of diet for individuals with SMA. Families are at risk of getting conflicting advice about elemental formulas from the internet and health professionals. Some articles published in the last three years have mentioned elemental formulas: Poruk and colleagues noted that more of the children in their study living over 18 months were receiving an elemental formula, Dr Hurst-Davis and colleagues from Utah, USA, who surveyed 44 individuals and their families with SMA Type 1, reported that several families reported ‘positive experiences’ with an elemental diet7. It is worth pointing out that neither of these studies were investigating elemental formulas or the possible benefits of receiving them, it may be a coincidence that more of those that lived over 18 months received an elemental formula or that only the families asked happened to have ‘positive experiences’. Neither study could give any conclusions on whether elemental formulas were likely to be beneficial. Both studies said a clinical trial is required to investigate them further. 

Vitamin D and Calcium

Vitamin D is a substance associated with good bone growth and health. It is present in many foods, including oily fish (i.e. salmon), eggs, and some breakfast cereals. The body is also able to produce some Vitamin D in the skin using sunlight; in the winter months Vitamin D deficiency is more common. 

It has been suggested that up to a quarter of healthy children in the United Kingdom have a Vitamin D deficiency. Studies have suggested that Vitamin D intake is insufficient in up to 75% of individuals with SMA Type 18, with low levels of Vitamin D detected in the blood in 36.7% of individuals with SMA Type 2 or 39. Supplementation of Vitamin D may improve bone strength in individuals with neuromuscular conditions.

Calcium is a substance which is vital in keeping bones healthy. It is present in dairy foods such as milk and yoghurt. The body is very good at keeping calcium in the blood at a level which is not too much and not too little. The body keeps the calcium at a steady level using several methods; one of these involves taking calcium out of bones, making bones less dense and therefore weaker. This is why, if you have normal blood levels of calcium, it doesn’t necessarily mean that you will have enough calcium in your body overall.

In individuals with SMA who are able to walk and those with other similar conditions, getting back to walking after a fracture may be very difficult. Bone strength and avoiding fractures are therefore both important for maintaining the ability to walk and weight bear for as long as possible. Joyce and colleagues wrote a review on bone health and neuromuscular conditions in 201210. They suggested that there was only one small study looking at Vitamin D deficiency in individuals with SMA, but this showed a significant difference in the thickness (density) of bones when individuals were given increased dietary supplementation. Several studies have shown that improvements in bone health have only occurred when both Vitamin D and calcium are increased.

Conclusion

Over the past three years there have been very few studies specifically looking at nutrition in SMA. Researchers have focussed on SMA Type 1, and are often reporting on what is currently happening in practice rather than setting up studies monitoring the effects of a specific change in part of a diet.

As mentioned at the beginning of this article, nutrition is very complicated; for all individuals with SMA there is a delicate balance to be struck between calories, fat, protein, and carbohydrate intake. In the study mentioned earlier by Dr Hurst-Davis and colleagues, they found that more of the individuals had their diet directed by a family member rather than by a professional. They strongly recommended regular dietician follow up of individuals with SMA and the tailoring of the diet to their individual needs. Also highlighted by studies over the past three years is the importance of appropriate vitamin and mineral supplements, provided by a physician, in improving bone health. Finally, elemental and specialist formulas have not been investigated in enough detail yet to say whether they are beneficial or not.

January 2016

References

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8. Aton J, Davis RH, Jordan KC, Scott CB, Swoboda KJ. Vitamin D intake is inadequate in spinal muscular atrophy type I cohort: correlations with bone health. Journal of child neurology. 2014 Mar;29(3):374-80. PubMed PMID: 23334077. Pubmed Central PMCID: Pmc4259287. Epub 2013/01/22. eng.

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