Updated date:

Solanine, Green Potatoes, Nightshades, and Arthritis

Linda Crampton is a teacher with an honors degree in biology. She enjoys exploring nutrition as well as the culture and history of food.

Potatoes are nutritious and often colourful vegetables that belong to the nightshade family.

Potatoes are nutritious and often colourful vegetables that belong to the nightshade family.

What Is Solanine?

Solanine is a toxic chemical found in members of the nightshade family, also known as the Solanaceae family. The chemical acts as a natural pesticide. Plants produce the substance to protect themselves from insects and fungi that attack them. Solanine and related chemicals have been found in potatoes, tomatoes, eggplants, peppers, and other nightshade plants (but not in black pepper, which belongs to a different plant group).

In sufficient concentration, solanine produces unpleasant and even deadly effects in humans. Luckily, foods generally don't contain enough of the substance to hurt us. The chemical's concentration is often increased in green potatoes, though, so they should be avoided.

Some people report that nightshade plants make their arthritis worse and have attributed this effect to chemicals in the solanine family. Scientists say that there is no experimental evidence that potatoes, tomatoes, and other nightshades have an effect on arthritis. It's possible that a specific nightshade may be problematic for some people, however, although the problem may not be due to solanine.

Eggplant, or aubergine, is another nightshade vegetable.

Eggplant, or aubergine, is another nightshade vegetable.

Green Potatoes and Their Potential Dangers

Solanine is classified as a glycoalkaloid. All parts of the potato plant contain the chemical, but the largest amounts are in the sprouts and in green potatoes. If a potato has sprouted, all the sprouts should be removed before the potato is cooked.

Green patches in potatoes represent areas where chlorophyll has been produced. Chlorophyll is the green pigment that plants use to absorb light energy and produce their food. The pigment is safe to eat. However, the presence of chlorophyll indicates that the potato, which normally grows underground, has reacted to the presence of light. The green colour is often accompanied by the production of solanine, which the exposed potato produces to protect itself from attack by pests.

To complicate matters, not all green potatoes contain a high level of solanine, although the risk is greatly increased, and potatoes don't have to be green to develop a lot of solanine.

A high solanine concentration can make potatoes taste bitter. Even without this bitter taste, we shouldn’t eat green potatoes because they may still contain enough of the substance to cause harmful effects.

Possible Symptoms of Solanine Poisoning

Solanine poisoning affects the digestive tract and the nervous system. Symptoms of mild poisoning may include:

  • headache
  • dizziness
  • a burning sensation in the mouth
  • stomach cramps
  • nausea
  • vomiting
  • diarrhea

Severe solanine poisoning can cause drowsiness, weakness, confusion, vision problems, hallucinations, weak pulse, low blood pressure, and rapid breathing. Solanine ingestion may be fatal if a large amount of the chemical is eaten. The symptoms of poisoning may appear within minutes after ingesting the chemical or may not appear until hours later.

Scientists agree that solanine is poisonous, but there is uncertainty about how much green potato must be eaten to obtain a harmful dose of the poison. This may depend on body mass and individual sensitivity as well as the solanine concentration in particular potatoes and the number of potatoes that are eaten.

The poison is found throughout the plant, but especially in green potatoes and new sprouts. Never eat potatoes that are spoiled or green below the skin. Always throw away the sprouts.

— NIH National Library of Medicine

Dealing With Green Potatoes

The Extension Department of Michigan State University has a web page describing how to deal with green potatoes. The department gives the following recommendations.

  • Completely remove sprouts and eyes from potatoes.
  • Completely remove any small green areas.
  • If there are more than a few small green areas, discard the potato.
  • If the potatoes are going to be given to children, discard ones with any sprouts or green areas. Children have a lower body mass than adults and are therefore more susceptible to experiencing problems from solanine.
  • If potatoes taste bitter, don't eat them.

In addition, the NIH (National Institutes of Health) says that potatoes that are green below the skin should be thrown away.

Like potatoes, bell peppers are nutritious nightshade plants and shouldn't be eliminated from the diet unnecessarily.

Like potatoes, bell peppers are nutritious nightshade plants and shouldn't be eliminated from the diet unnecessarily.

How to Reduce the Solanine Level in Potatoes

Always check for green spots on potatoes before you buy them. It’s better to buy loose potatoes instead of bagged ones, since it’s easier to check the loose vegetables for green areas. It’s also easier to check whether brown or yellow potatoes have turned green than to check red or purple varieties. If you grow potatoes, check that they stay covered by soil as they develop. When you're storing potatoes in your home, keep them in a cool and dark place to reduce solanine formation.

Once potatoes are cooked, solanine can no longer form because essential enzymes needed for its production are destroyed. However, any solanine made before the potatoes were cooked will remain. The chemical isn't destroyed by boiling, steaming, baking, microwaving, or frying potatoes. Deep frying at very high temperatures partially destroys the chemical.

Diet and Arthritis

Scientists say that there is no connection between arthritis and eating specific foods, or at least that there is no evidence for this connection. Research suggests that a healthy diet filled with vegetables, fruits, fibre, and essential fatty acids may dampen inflammation and reduce arthritis pain. The idea that some foods such as nightshades or the solanine within them can trigger arthritis pain is controversial.

Some people say that their joint pain is worsened when they ingest nightshade plants or a specific member of the nightshade group. At the moment the evidence for this link is anecdotal, not experimental. The effect seems to be strongest for people who suffer from rheumatoid arthritis. Even if nightshades affect some people with arthritis they may not affect everyone with the disorder, however.

In addition, although solanine is often assumed to be the culprit by people who support the nightshade and arthritis theory, there is no proof that this is true. If a nightshade plant does cause pain, this may be due to a reason other than the presence of solanine.

Some health organizations say there is no link between nightshades and arthritis pain while others say that there might be a link for some people.These different viewpoints are described in the articles mentioned in the "References" section below,

Tomatoes are a nutritious and delicious food. They belong to the nightshade family of plants.

Tomatoes are a nutritious and delicious food. They belong to the nightshade family of plants.

My Experience With Tomatoes and Joint Pain

I have osteoarthritis in my neck, but as far as I know I have no osteoarthritis in my elbows and no rheumatoid arthritis. A few years ago I went through a period when I developed elbow pain whenever I ate tomatoes, however. The effect was obvious and consistent, so I avoided tomatoes for a while. The pain disappeared. Many months later I tried eating tomatoes again. This time there were no problems.

Scientists say that the solanine-like chemical in tomatoes is not really solanine but instead is a related chemical called tomatine. The problem that I experienced after eating tomatoes may have had nothing to do with tomatine, though. In addition, the fact that the problem was only temporary suggests that it may have been controlled by variable factors such as the type of tomatoes that I ate or the state of my intestinal lining at the time. It did show me that tomatoes can influence joint pain under some conditions, though, at least in my body.

Tomatillos also belong to the nightshade family.

Tomatillos also belong to the nightshade family.

Elimination or Exclusion and Challenge Diet

If you have arthritis, an elimination diet could be used to discover whether foods in the nightshade family affect your condition. If you decide to go on this diet, you must ensure that you eat nutritious food. Foods from nightshade plants contain some valuable nutrients. It's important to obtain as many as these nutrients as possible from other foods if a nightshade is eliminated from the diet.

An elimination diet is sometimes known as an exclusion and challenge diet. When the diet is followed, a food is temporarily excluded from the diet and observations are made about the body’s response to the elimination. After the elimination period, the food is eaten again (the "challenge" part of the diet) to see if symptoms return.

This is a type of cayenne pepper, which is a member of the nightshade family.

This is a type of cayenne pepper, which is a member of the nightshade family.

How to Follow an Elimination Diet

Choose only one food to temporarily eliminate from your diet. A different trial is needed to test another food. While you are on the diet, keep a daily record of what you eat and how your arthritis responds.

After a three to four weeks on the diet, you should assess the results. The eliminated food should be reintroduced for several days to see if symptoms reappear or worsen. If they do, then you’ve probably found a food that you’re sensitive to. By eliminating that food from your diet your symptoms should improve.

If your pain doesn't improve on the elimination diet and reintroducing the food makes no difference to the intensity of your pain, then you know that the food that you eliminated doesn’t need to be removed from your diet.

In the video above, a registered dietitian explains why people with arthritis should eat certain foods and avoid others. It's interesting that nightshades are on her avoid list, yet unlike the case for the other foods she doesn't discuss them. Perhaps this reflects the controversy about nightshades and their effects.

Rheumatoid Arthritis and Nightshades Poll

Potential Problems With Elimination Diets

Elimination diets can be time consuming to carry out. A food must be removed from the diet for several weeks so that all traces of the food and its metabolites can be removed from the body. In the case of a nightshade exclusion diet, it also takes time to discover if only one nightshade or if all nightshades need to be eliminated from the diet. A person may discover that some nightshades need to be restricted to occasional ingestion instead of being completely eliminated from the diet.

Nightshade vegetables have great nutritional and health benefits. It's important that you don't eliminate any of them from your diet (except during a short-term exclusion diet) unless this is necessary to reduce pain.

Despite the potential problems, an elimination diet could be very helpful. The time and effort required to determine whether foods affect your arthritis and to identify the specific foods that cause problems could be well worthwhile if the result is pain reduction or relief.

References

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2010 Linda Crampton

Comments

Linda Crampton (author) from British Columbia, Canada on May 13, 2014:

Thank you very much for the comment and the vote, ologsinquito. I appreciate the share, too!

Linda Crampton (author) from British Columbia, Canada on May 13, 2014:

Hi, MJ. Thank you very much for the comment. I'm sorry about the amount of joint pain that you experience. I hope very much that you find a way to reduce your pain, whether it's a dietary method or some other way. Best wishes and good luck to you!

Linda Crampton (author) from British Columbia, Canada on May 13, 2014:

Hi, Peg. I'm careful with my potatoes too! I check the ones that I buy carefully and try to store them properly. Thanks for the visit.

Marcy J. Miller from Arizona on May 13, 2014:

Alicia, I have a feeling I'll be eternally grateful to you for this valuable information. I was aware of the dangers of eating green-spots in potatoes, and I know a local raw-food chef who refuses to serve any nightshade plants due to her strong belief they are unhealthy. However, I never knew about the relationship to joint pain. I suffer from severe joint pain (particularly in shoulder and elbow at present) and have significant degeneration in my hips, knees, and neck. It has recently been made much worse by some injuries I incurred in December (and was already aggravated by another horse wreck I'd had seven years ago). I do eat a lot of tomatoes and a moderate amount of potatoes -- and now I will pay attention to see if they increase the pain. This is fascinating stuff and perhaps it will help me out quite a bit. Thank you!

Best -- Mj

Peg Cole from Northeast of Dallas, Texas on May 13, 2014:

Quite a useful reminder here AliciaC. Thanks for bringing this important information out into the light. I'll be keeping my potatoes in the dark from now on.

ologsinquito from USA on May 13, 2014:

This is very useful information. I try to keep my potatoes out of the light, and make sure to cut off as much green as I can, when I see it. Voted up and shared.

Linda Crampton (author) from British Columbia, Canada on December 21, 2012:

Thanks for the detailed comment, Chuck. My local stores do a good job of removing potatoes with green spots, too. Potatoes keep well in a cool, dark place for several months, although I've never tried storing them for six months! Like you, I buy organic colored potatoes, because they have extra nutrition compared to regular brown potatoes. It is very interesting that potatoes contain nicotine, although luckily it's a small amount!

Chuck Bluestein from Morristown, AZ, USA on December 21, 2012:

I think that the stores do a good job of getting rid of potatoes that are not good since they do not want someone reporting getting sick from eating their potatoes. I just read an experiment from decades ago where a couple ate potatoes and oil for 6 months and they had no problems from doing that.

I do not eat the cheap brown potatoes. I eat the red potatoes, the golden potatoes or the purple potatoes and it is important to get them organic since they are sprayed with pesticides more than other foods. But it is good to know that if the potatoes are around too long, the eyes (sprouts) start to grow and you need to remove them. Nightshade plants also contain nicotine like another nightshade plant-- tobacco.