May 9, 2013

expert reaction to new research into eating red peppers and Parkinson’s disease

Research in Annals of Neurology found that Solanaceae, a family of plants including peppers and tomatoes may provide a protective effect against Parkinson’s disease due to the plants containing low levels of nicotine. A before the headlines analysis accompanied this roundup.

Catherine Collins, Principal Dietitian, St George’s Hospital NHS Trust, said:

“The authors of this study add to the knowledge that a diet rich in plant antioxidants and low in inflammatory fats – a ‘Mediterranean style’ diet – is protective against Parkinson’s Disease (PD), an irreversible condition for which there is currently no cure. This study built on previous research that showed smokers to have a lower risk of PD, attributed to nicotine possibly having a protective effect on brain cell function.

“People are often surprised to know that nicotine is found in variable amounts in the ‘deadly nightshade’ family of plants (potatoes, tomatoes, peppers, chillies, and aubergine – plus cauliflower, which isn’t a member of this family group).  In this study the researchers used a standard food questionnaire to examine the frequency (note – not the actual amount) of vegetable nicotine intake of PD sufferers compared to the general population.

“Despite strong suggestion that nicotine – from any source – may prove beneficial, the results of this study prove disappointing for a dietitian, with frequent pepper consumption showing a weak association with PD protection, but of insufficient robustness to promote peppers as a protective food against PD.

“Why should this be the case? Nicotine content can vary in vegetables due to growing conditions, storage, harvest and cooking method. For example, the nicotine content of a green tomato is ten times higher than a ripe tomato. Nicotine is poorly absorbed and we don’t really know enough about how other foods interact with the plant nicotine to influence its effect in the body.

“As the authors neatly explain in the discussion section, the devil is in the detail. Plants that we eat contain thousands of biologically active constituents, many of which have potential for protecting us against chronic disease. We also choose to eat plants in a variety of ways – which may also influence the effect on our health. Peppers and chillies are rarely eaten alone, and it may be the foods cooked with these vegetables that confer some protection. 

“As this and other research has demonstrated over the last decade, it’s impossible to pull out one vegetable, or a group of vegetables, as independently beneficial to health. The Mediterranean diet is more than the sum of its parts. At the moment, we can’t identify exactly what it is in the diet that does us so much good, only that we know it does.”

Claire Bale, Research Communications Manager at Parkinson’s UK, said:

“The researchers studied several vegetables that contain tiny amounts of nicotine including peppers, which have the most, as well as tomatoes and potatoes. They found that people who reported eating peppers at least twice a week were around 30% less likely to develop Parkinson’s. This may sound significant, but because the risk of developing Parkinson’s in the general population is already quite low (around 1 in 500), this reduction in risk is actually smaller than it sounds.

“This was a small study which involved just over 1000 people and to produce convincing results, these types of studies really need to involve much larger numbers – tens to hundreds of thousands. It also studied a relatively young group of people, the average age was mid-60s, when Parkinson’s is a condition which often develops much later in life.

“At the moment we don’t fully understand the causes of Parkinson’s and we don’t know of anything which can prevent the condition, although there are a number of factors that may slightly lower risk including smoking cigarettes, drinking coffee and exercise.

“Although this study offers some interesting clues about how diet may affect risk of Parkinson’s developing, we need much larger studies in older populations before we know whether eating peppers can be added to this list.  Currently, there’s no evidence that eating certain foods containing nicotine can slow Parkinson’s progression”.  

Professor K Ray Chaudhuri, Consultant Neurologist and Professor in Neurology / Movement Disorders, King’s College Hospital, said:

“Nielsen et al report an interesting study addressing risk of Parkinson’s disease (PD) and diet. They report, in a controlled study, that eating edible vegetables from the Solanaceae family (particularly peppers), allied to dietary nicotine, reduced the risk of developing Parkinson’s. This study adds to a number of studies that have reported various factors that may reduce or increase the risk of PD or symptoms such as dyskinesias, ranging from insecticides and pesticides to coffee and beer drinking.

“Nicotine has been previously studied and has a complex relationship with PD. A neuro-protective effect has been postulated and the MJ Fox foundation has embarked on a large trial, the NIC-PD, to address whether nicotine patches may have a protective effect against PD. If supported by further studies that show the same association, this dietary study would certainly add weight to this evidence base and for the first time, provide a reasonable evidence base for dietary intervention in PD. However, as the authors state, there may be many confounders of the observed effects, most notably alternative agents contained in pepper as well as the amount of effective nicotine that may be delivered to the brain from dietary nicotine containing vegetables, given there is delayed gastric emptying and absorption issues which may be present even in the very early stages of PD. Furthermore, studies in animal models have been disappointing with respect to motor effects of nicotine and previous studies in Parkinson’s have produced contradictory results. However, the controlled design as well as inclusion of a group of well characterised patients is a strength of this study. As the authors say, we have to regard these results with interest, but have to wait till large scale studies such as NIC-PD report their data.”

Professor John Hardy, Professor of Neuroscience, UCL, said:

“The trouble is in epidemiology studies one compares many factors against many outcomes.  Because so many tests are done but only the positive ones are reported it is difficult to assess their true significance.  The association reported here between eating red peppers and risk of developing Parkinson’s disease is almost certainly a false positive and not worth making a fuss about.”

‘Nicotine from edible Solanaceae and risk of Parkinson’s disease’ by S Nielsen et al., published in Annals of Neurology on Thursday 9th May.