Vitamin deficiency and the PNS

Rhys Roberts is a consultant neurologist at Addenbrooke's hospital in Cambridge and also a researcher on the peripheral nervous system. Katie Haylor asked Rhys how important diet is to peripheral nervous system health...

Rhys - My main interest is in the inherited forms of peripheral nerve diseases. So these are chronic conditions that are usually due to mutations in a number of genes of which now there are over a hundred. But I also see people who present usually later on in life with what we call acquired peripheral nerve problems, or sometimes called neuropathies - again, there are lots of different causes for that.

Katie - Is nutrition a particularly relevant factor when you're thinking about peripheral nervous system damage? Be it inherited or acquired.

Rhys - Nutrition is a very important factor to consider when approaching someone who presents with a peripheral neuropathy. It's been known for centuries that sailors, for example, who were coming back from the far East, eating only a rice-based diet would develop weakness and sensory change in their legs. And it wasn't until the early 20th century where deficiency in vitamin B1, also known as thiamine, was found to be the cause. And this led to the further discovery of a number of other vitamins, all of which have their distinct effect if they're lacking in the diet and can have an effect on the nervous system, but particularly the peripheral nervous system, causing a neuropathy. So this is a key thing that we explore and measure in anyone presenting with weakness and sensory change or numbness in the legs and arms.

Katie - So it sounds like that's a lack of an ideal diet, for instance in the case of the sailors you were mentioning. But what about if you've inherited a peripheral nervous system issue?

Rhys - There are a small number of inherited forms of neuropathy which are due to the lack of the ability to process or use particular vitamins. And that can present with imbalance, neuropathy and particularly thinking of vitamin E, which can mimic a condition called cerebellar ataxia and neuropathy, which is an imbalance where there's a problem with a part of the brain that's involved in the coordination of your limbs. And there are also deficiencies in the way of processing other vitamins as well, which can mimic being deficient of this in your diet.

Katie - It's interesting you made that distinction because it's one thing to be lacking a particular nutrient in your diet, but it's quite another to not be able to use it in the body in the way that you need to.

Rhys - That's right. Often you need to appreciate that. And sometimes you need to bypass where the so-called block is in the mechanism of processing these vitamins, in order to actually treat and reverse the symptoms and signs.

Katie - So where is this absorption happening, then?

Rhys - The absorption of the vitamins occurs in the gastrointestinal tract and there are distinct areas and parts of the intestine that appear to be responsible for the absorption of these vitamins in conjunction with chemicals that are secreted and produced by the stomach and the pancreas.

Katie - Does that then suggest that if you have an issue in your gastrointestinal system, that could lead to a problem with absorbing these vitamins?

Rhys - That's right. Yes. When we first discovered the importance of nutrition and vitamins in a healthy nervous system, as I say, usually in the context of malnutrition or very restricted diets. We have become much more aware that if there are problems in the absorption of these vitamins - usually acquired so these are things that come on in life - that can present with symptoms of a neuropathy. One of the increasingly recognised situations where we see this very commonly now is in the context of bariatric surgery. Very effective interventions, such as surgery, that help with weight loss. And in fact can reverse conditions such as type two diabetes and obesity. We see that these forms of surgery, which often reconnect various parts of the gastrointestinal tract can impair the absorption of particular vitamins.

Katie - How can you mitigate against those ill effects, if someone's having bariatric surgery?

Rhys - It's an increasingly recognised problem as the number of interventions are increased. There are some estimates that around about 16% per year of people undergoing these treatments can develop neurological complications. And most of these is due to not absorbing enough of the required vitamins to keep a healthy nervous system. So increased recognition is key, uh, including getting specialist dieticians measuring these vitamins and elements in your blood and supplementing accordingly.

Katie - Is diet and nutrition an important part of the conversation you would tend to have with your patients who you were looking after, who might have a peripheral nervous system issue?

Rhys - It is. Certainly those who are deficient, and in the clinic most commonly we will see people with vitamin B12 deficiency, which is a relatively common as a cause. Eating a balanced diet clearly is a very important step for both neurological health and also general wellbeing. We do see in the neurology clinic, certain conditions which makes eating very difficult. For example, the motor neuron diseases often cause difficulties for people with their speech, but also with their swallowing, which means they can't eat a normal diet safely and need different texture of foods. They also need to maintain their calorific value in smaller amounts. So this needs expert dietetic input. Additionally, if the swallow is deemed so unsafe in that food tends to, instead of going down the oesophagus, will go into the lungs causing a pneumonia, we can offer insertion of a tube directly into the stomach where we can add food which is balanced and supplemented directly into the stomach. Meaning the person doesn't have to eat but can maintain the required vitamins and minerals and elements that you need for healthy living.

Katie - Is there evidence linking particular dietary habits to protection against peripheral nervous system issues? Because you've mentioned some [dietary] vulnerabilities, and I'm wondering if there's an upside to this?

Rhys - In terms of evidence, it's difficult to support specialist diets other than eating a well balanced diet containing everything that's recommended in recommended amounts. What we've begun to do certainly in the motor neuron diseases is to work in different centres across the UK to study the nutritional intake in people living with these conditions, looking at different ways of focusing, calculating calorific and nutritional need, as opposed to the standard care with a dietician, and seeing if one is more beneficial than the other.

Katie - It sounds like what you're saying is a generally healthy diet is going to be good for your nervous system. And that at the moment there isn't a thoroughly evidence-based kind of pro nervous system diet.

Rhys - That's right. And there isn't any solid evidence that we can turn to that would support any particular diet over the other, which has a role in everyday management of people with neurological diseases.

Katie - Do you have any sort of general nutritional advice above and beyond what we've just talked about that you think might be worth mentioning?

Rhys - So in general, my approach to the people that I see is to support and suggest a well balanced diet, supplemented if needed and if clinically indicated. But I would always be cautious regarding following particular diets that purport to cure or magically reverse a chronic neurological condition. Firstly, because of the lack of clear evidence. And secondly, some of the supplements can prove very costly. So my advice is to take a general approach, a common sense approach, but to make sure that you're ticking the boxes of vitamins.