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Caffeine Facts, Actions, and Effects in Humans and Bumblebees

Linda Crampton is a writer and experienced science teacher with an honors degree in biology. She enjoys writing about science and nature.

Coffee is many people’s favourite source of caffeine.

Coffee is many people’s favourite source of caffeine.

An Interesting and Useful Chemical

Caffeine is an interesting chemical that can have major effects on our bodies. It’s produced by multiple plants and affects other organisms besides humans, including bumblebees. In humans, it’s a central nervous stimulant. It has both benefits and drawbacks for us. Scientists have discovered that caffeine ingestion can significantly weaken an infection by a fungus called Nosema bombi in bumblebees. This discovery could be very significant because N. bombi has been linked to serious problems in bee colonies. The insects are important pollinators.

Sainfoin plants grow in the wild in the area that the scientists explored. The nectar produced by their flowers contains caffeine. In some of the sainfoin plants in the surrounding area, the concentration of caffeine in the nectar matched the one used in the experiment performed by the scientists. Other plant species also produce nectar containing caffeine. These facts suggest that if specific plants are grown in bumblebee habitats, they might help the insect fight the fungus.

Sources of Caffeine and Functions in Plants

The coffee plant (Coffea arabica) provides much of the coffee that humans drink. The Coffea genus contains many species, some of which are known to contain caffeine. Other plants containing the chemical include tea, cocoa, yerba mate, guarana, species that produce kola nuts (genus Cola), and yaupon holly. The last species is native to North America.

Coffee is made from the seeds inside the fruits of coffee plants. The fruits are called berries or cherries. The seeds are known as coffee beans. The fruit usually produces two seeds. They are roasted to produce the coffee flavour and taste that many people enjoy.

Scientists are still exploring the reason why plants make caffeine. The leading idea seems to be that, at least in seeds, the chemical acts as a pesticide, especially against larval insects. Caffeine in nectar appears to have a different function. Some pollinators seem to remember and appreciate the caffeine-infused nectar and visit the flowers that produce it more often than other ones. This increases the chance of the flower being pollinated.

A ball-and-stick model of a caffeine molecule

A ball-and-stick model of a caffeine molecule

In the illustration above, black = carbon atoms, blue = nitrogen, red = oxygen, and white = hydrogen. The links between the atoms represent chemical bonds. Double lines represent double bonds. The dashed lines indicate that the bond is intermediate between a single and a double bond.

Structure and Chemical Name of Caffeine

Caffeine is a member of a group of chemicals known as methylxanthines. Xanthines have two fused rings in their structure, as shown in the illustration above. Caffeine’s chemical name is 1,3,7-trimethylxanthine. The formula of a methyl group is CH3. Caffeine contains three methyl groups.

The carbon atoms in an organic compound are numbered according to certain rules, which are beyond the scope of this article. The numbers of the carbon atoms that have a particular significance are placed at the front of a compound’s name, as in caffeine’s chemical name. When a chemist or organic chemistry student sees the name of an organic compound, they know some major facts about the molecule’s structure even without seeing an illustration.

Actions of Caffeine in the Human Body

Caffeine is an impressive chemical that has multiple actions in the human body. I describe some major aspects of its behaviour below. Some of the chemical’s functions are well understood, but others aren’t. Caffeine’s effects can be very helpful for some people but are problematic for others.

The Blood-Brain Barrier

Caffeine is able to cross the blood-brain barrier. This barrier protects the brain from harmful substances. Blood vessels are lined by endothelial cells. In the brain, these cells are very close together and form what is known as a “tight” junction. The layer of cells prevents many substances from entering the brain while allowing the entrance of essential ones.


Caffeine binds to the adenosine receptors on brain cells. It’s able to do this because it bears some similarities in structure to an adenosine molecule. Adenosine reduces neural activity and makes us feel sleepy. Its concentration is highest when we have stayed awake for a long time. Caffeine blocks the chemical from reaching its receptor, which keeps us alert.


Caffeine triggers the pituitary gland to stimulate the adrenal glands. The glands release adrenaline (also known as adrenalin), which triggers alertness in several ways. It increases the heart rate and blood pressure, triggers the air passages in the lungs to expand, dilates the pupils of the eyes, causes an increased amount of blood to flow to the muscles, and raises the blood glucose level so that the brain can obtain more energy. These changes help the body to deal with an emergency. The set of changes is sometimes known as the fight or flight response.


Caffeine enhances the action of dopamine. The substance is a neurotransmitter. Neurotransmitters are released at the end of one neuron (or nerve cell) and join the next one. They may transmit the nerve impulse to the second neuron (an excitatory neurotransmitter) or prevent its passage (an inhibitory neurotransmitter). Dopamine is both excitatory and inhibitory, depending on where it acts. It’s sometimes referred to as the “pleasure chemical,“ but many researchers say that this idea is too simplistic. The information in the quotation below seems to be more accurate. The quote demonstrates why caffeine is often classified as a psychoactive drug.

Dopamine plays a role in how we feel pleasure. It's a big part of our unique human ability to think and plan. It helps us strive, focus, and find things interesting.

— WebMD

Potential Problems Caused by Caffeine

Caffeine is often a safe and helpful substance for humans. It can sometimes have unpleasant or even harmful effects, however. At very high doses, it’s dangerous for everyone. The illustration above shows the most common effects of a caffeine overdose. Some people are more sensitive to the chemical than others and must drink caffeinated beverages in small amounts or completely avoid them.

Due to individual sensitivity, the existence of specific illnesses, and the potential for harm at high doses, anyone who is thinking of using caffeine for a health problem should seek a doctor’s advice. The relevant WebMD article referenced at the end of this article could be helpful, but it’s still important to consult a physician.

A worker buff-tailed bumblebee (Bombus terrestris)

A worker buff-tailed bumblebee (Bombus terrestris)

The Nosema Fungus in Bumblebees

Several species of Nosema have been implicated in the decline of bumblebee (or bumble bee) populations. Nosema bombi is most often linked to the decrease in their numbers, and its name is linked to them. Bumblebees belong to the genus Bombus. The insects are important pollinators of plants, so their decline is worrying.

There may be several factors causing the population problem. The presence of Nosema bombi is thought to be either one of multiple conditions causing a colony’s decline or, in some cases, to be entirely responsible for the problem. Research is continuing in order to better understand the situation.

Nosema belongs to the phylum Microsporidia. The species in the phylum are obligate intracellular parasites—that is, they must enter a cell of their host in order to complete their life cycle. Nosema is unicellular and microscopic. It doesn’t have the typical features of most fungi. Biologists say that the evidence obtained so far indicates that the genus should be classified as a fungus, however. The species in the genus absorb nutrients from their host cell and reproduce by means of spores.

Wild bumble bees are experiencing population declines globally. Causes of declines in North American populations are unclear, although declining species are more frequently infected by the pathogen Nosema bombi.

— Cameron et al, via PNAS

According to the Merriam-Webster dictionary, the etymology of the word sainfoin is as follows: “French, from Middle French, from sain healthy (from Latin sanus) + foin hay, from Latin fenum.” They say that the word should be pronounced “sane-fo-in” with an emphasis on the first syllable.

Facts About Sainfoin Plants

Sainfoin is the common name given to a group of plants in the genus Onobrychis. The most common species grown in the UK (where the bumblebee research was conducted) appears to be Onobrychis viciifolia. The species is native to Europe and Asia but has been planted in North America. The plant is often grown to create hay for farm animals. The hay is said to be highly palatable for them.

The plant is a member of the family Fabaceae, which was once known as the family Leguminosae. The members of the family are often referred to as pulses. Sainfoin is a perennial plant that produces lovely pink flowers in spikes. The writer of the sainfoin article referenced below says that the flowers are a magnet for insects. Their nectar is very attractive to both bumblebees and honeybees.

Like other legumes, the plant has root nodules where nitrogen-fixing bacteria live. Nitrogen fixation is the process in which atmospheric nitrogen (N2) is converted into a form that plants and animals can use, such as ammonia. The bacteria benefit from the relationship by receiving carbohydrates from the plant.

A queen buff-tailed bumblebee on a small-leaved lime flower

A queen buff-tailed bumblebee on a small-leaved lime flower

Bombus terrestris is known as the buff-tailed bumblebee or the large earth bumblebee. The small-leaved lime in the photo above has the scientific name Tilia cordata.

The Caffeine and Sainfoin Nectar Experiment

Scientists from two British institutions investigated the effect of caffeine on Bombus terrestris. The researchers are associated with Royal Holloway University of London and the Royal Botanic Gardens, Kew. They say that in some parts of the world, bumblebees provide ”up to 80% of pollination services for some crops.” A severe decrease in their numbers could have serious effects.

Bees are known to remove sick larvae from a colony, which helps to protect the remaining individuals. According to the researchers, however, the insects are unable to detect that larvae contain N. bombi.

The researchers analyzed the chemicals present in both the pollen and the nectar of sainfoin flowers in the study area. They found caffeine in the nectar. The scientists then explored the effect of caffeine on the bees. They discovered the following facts.

  • Captive bumblebee colonies with wild-caught queens had a lower prevalence and intensity of infection when given caffeine.
  • Wild bumblebee colonies that were exposed to caffeine in sainfoin had a reduced incidence of infection compared to those not exposed to caffeine.

In the first experiment mentioned above, the scientists used the highest concentration of caffeine detected in the sainfoin nectar in their study area. The caffeine was administered in the form of sugar water. In their report (referenced at the end of this article), the researchers made the statement shown below with respect to their investigation.

While this was the highest concentration (of caffeine) recorded in our analyses, from a limited number of sampling points and locations, it was representative of natural caffeine concentrations reported elsewhere in floral nectar.

— Arran J. Folly, Hauke Koch, Iain W. Farrell, Philip C. Stevenson and Mark J. F. Brown

How Does Caffeine Influence the Infection?

While the administration of caffeine didn’t eliminate the fungal infection in bumblebee colonies, it did have noticeable and significant benefits. Both prophylactic treatments intended to prevent disease and therapeutic treatments for infected individuals were helpful in the experiment.

It’s not yet known how caffeine produces its benefits in bees, but researchers have two theories. One is that the caffeine reduces spore formation by N. bombi. The other is that the substance triggers the expression (or activity) of bee genes that provide immunity.

The study results are interesting and are potentially very significant. Further research is needed; however, scientists suggest that plants known to produce nectar containing caffeine should be planted in areas where bumblebees forage. This seems like a good step to follow even before more research is performed. It might be helpful to choose plants that flower at different times. Sainfoin plants could be a useful addition to an area that bumblebees explore.

Important Research and a Hopeful Discovery

Investigating the action of caffeine in the human body is important because the substance has many effects. It’s believed to reduce the risk of some diseases, which could be a major benefit of the chemical. On the other hand, it can cause unpleasant symptoms in some people. The dose and individual susceptibility are vital factors to consider with respect to its effects.

The discoveries about the relationship between caffeine, sainfoin, and a fungus that affects bumblebees are interesting. Additional research and discoveries could be helpful, but the knowledge gained so far could be very significant. Saving bumblebees (and honeybees, which are also in trouble) is an important endeavour. Researchers say that honeybees are also attracted to the sainfoin plant, and other species of Nosema can affect these insects. I haven't read about any research linking caffeine from sainfoin to the intensity of a fungal infection in honeybees, however. It's an intriguing thought that could be worth investigating.


  • Functions of caffeine in the plants that make the chemical from Scientific American
  • The caffeine molecule and some of its actions in the human body from PubChem (part of the NIH, or National Institutes of Health)
  • Neurotransmitters and the brain (including the role of caffeine) from McGill University
  • Information about caffeine from StatPearls and the National Institutes of Health (NIH)
  • Dopamine information from WebMD
  • Caffeine uses and precautions from WebMD
  • The invasive pathogen hypothesis of bumble bee decline from PNAS (Proceedings of the National Academy of Sciences of the United States of America)
  • Information about the phylum Microsporidia from PLOS Pathogens
  • Sainfoin facts from the Soil Association (a registered charity in the United Kingdom)
  • Nectar chemistry can suppress the social epidemiology of parasites in an important pollinator from Proceedings of the Royal Society

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.

© 2021 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on June 03, 2021:

Thank you very much, Deejay.

Deejay Mash from United States on June 03, 2021:

Great read, and very valuable info as well.

Linda Crampton (author) from British Columbia, Canada on June 02, 2021:

Hi, Fran. Yes, nature is amazing! Caffeine is a very interesting chemical.

Linda Crampton (author) from British Columbia, Canada on June 02, 2021:

Thank you very much, Devika. I enjoy drinking coffee, though I don’t do it regularly. It’s an interesting beverage.

fran rooks from Toledo, Ohio on June 02, 2021:

Alicia, great article. I am a true coffee lover and never knew about the relationship between bees. Nature is indeed a miracle.

Devika Primić from Dubrovnik, Croatia on June 02, 2021:

Hi Linda interesting facts about these effects. I drink coffee twice a day and knowing that about bees is extraordinary. Thank you for this fascinating hub, Always well-researched and lots to learn from your hubs.

Linda Crampton (author) from British Columbia, Canada on May 31, 2021:

I agree, Flourish. The factors that help pollination occur are very important.

Linda Crampton (author) from British Columbia, Canada on May 31, 2021:

Hi, Vidya. Nature is certainly amazing! Human biology is, too. I’m looking forward to future discoveries about caffeine with respect to us and bees.

FlourishAnyway from USA on May 31, 2021:

Anything that helps bees I am in favor of. I don’t drink coffee at all but we all benefit from pollinated crops.

VIDYA D SAGAR on May 31, 2021:

Fascinating that the caffeine in flower nectar can protect bumble bees and bees from fungal infections. Nature"s defense mechanisms to protect it's species is really amazing. I wasn't aware that caffeine can cross the BB barrier. No wonder we feel so refreshed and active after having a cuppa. Very informative and interesting article Linda. Thanks for sharing.

Linda Crampton (author) from British Columbia, Canada on May 31, 2021:

Thanks, Mary. I appreciate your visit and comment.

Mary Norton from Ontario, Canada on May 31, 2021:

Thank you, Linda. I appreciate learning more about the effects of caffeine not just on us but other living creatures around us.

Linda Crampton (author) from British Columbia, Canada on May 31, 2021:

Hi, Alyssa. I appreciate your visit. The link between caffeine and bees is promising. I hope more research is done soon.

Alyssa from Ohio on May 31, 2021:

I often joke that my blood type is caffeine. I love coffee and it keeps me going during the day. This was a fascinating article! I never considered the effect caffeine might have on other animals, let alone pollinators. The fact that it could help bees is both interesting and promising.

Linda Crampton (author) from British Columbia, Canada on May 31, 2021:

Hi, Peggy. It would be wonderful if caffeine helped bees. I hope the research continues. Thank you for the comment.

Linda Crampton (author) from British Columbia, Canada on May 31, 2021:

Hi, Bill. Coffee has drawbacks as well as benefits, but if you like the taste, it may be worth drinking. Thanks for the visit.

Linda Crampton (author) from British Columbia, Canada on May 31, 2021:

Hi, Chitrangada. Thank you for the comment. I drink coffee in moderation, too. I Like it, but I mustn’t drink too much.

Peggy Woods from Houston, Texas on May 31, 2021:

What a fascinating article! It would be wonderful if planting more caffeine-producing plants could help stop the decline in bee colonies. You always serve to educate us about things that we may not know. Thanks!

Bill De Giulio from Massachusetts on May 31, 2021:

Great information, Linda. I’m not a coffee drinker but I find it interesting that there may be health benefits from caffeine. Perhaps I should start drinking coffee? And the possible benefit of caffeine to bees should definitely be pursued further. Thanks again for the education.

Chitrangada Sharan from New Delhi, India on May 31, 2021:

An informative and well researched article and I learnt a lot from it.

I do take coffee, but in moderation. You have made some important points, which the caffeine lovers should keep in mind.

Thank you for sharing another excellent article.

Linda Crampton (author) from British Columbia, Canada on May 31, 2021:

Thanks, Eman. I appreciate your visit.

Eman Abdallah Kamel from Egypt on May 31, 2021:

Thank you, Linda, for this detailed article on caffeine. I enjoyed reading it very much.

Linda Crampton (author) from British Columbia, Canada on May 30, 2021:

Thanks for the comment and for sharing your experiences, Liz. Caffeine and its effects are very interesting topics.

Liz Westwood from UK on May 30, 2021:

This is a fascinating and, as ever, well-researched article. I have learnt a lot more about caffeine from it. I have noticed that, with age, I have had to reduce my caffeine intake. After mid-afternoon I avoid caffeine as it affects my sleep pattern. A later dose of caffeine and sleep eludes me.

Linda Crampton (author) from British Columbia, Canada on May 30, 2021:

Thank you for the visit and the comment, Rozlin.

Rozlin from UAE on May 30, 2021:

This is a well researched article, Linda. I learned a lot about caffeine from your article. Thanks for sharing.

Linda Crampton (author) from British Columbia, Canada on May 30, 2021:

Thanks for the visit and the comment, John. I hope the studies of the effects of caffeine in plants do lead to the defeat of the fungus.

John Hansen from Australia (Gondwana Land) on May 30, 2021:

A very interesting article, Linda. I probably drink around three cups of coffee per day on average. I wouldn’t consider that excessive but i an drinking more than I used to. Hopefully the studies of the effects of caffeine producing plants on Bumblebees does lead to the eventual defeat of the Nosema Bombi infection.

Linda Crampton (author) from British Columbia, Canada on May 30, 2021:

I sometimes start my day with a cup of coffee, though not always. It can be a nice drink to accompany breakfast. The relationship between bees and caffeine is interesting.

Linda Crampton (author) from British Columbia, Canada on May 30, 2021:

The blood pressure effect sounds horrible, Misbah. Like you, I make my coffee very milky.

Blessings to you as well. I hope you have a wonderful week.

Misbah Sheikh from — This Existence Is Only an Illusion on May 30, 2021:

Thank you so much for sharing this informative article, Linda. I am a big fan of tea. I drink almost 8 to 10 cups of tea daily but coffee doesn't suit me. I remember last time when I had coffee from a cafe in Barcelona maybe it was very strong or something but suddenly after 1 or 2 hours my Blood Pressure shoot up to 150/90. After that, I always try to avoid taking coffee from cafes but I add it sometimes in boiling milk and take it in the winter evenings.

The information you shared about bees is very interesting. I enjoyed reading it and have learned a lot from your article today for this I am thankful.

God Bless you and keeps you safe

Blessings and Love

Linda Chechar from Arizona on May 30, 2021:

Coffee is different that is cup in the morning breakfast. The bees are the colonies that are comments information!

Linda Crampton (author) from British Columbia, Canada on May 30, 2021:

Thank you very much for the kind comment, Pamela. I drink coffee, but I have to limit the amount that I drink or I experience unpleasant effects.

Pamela Oglesby from Sunny Florida on May 30, 2021:

This is a fascinating article, Linda. I drink about a cup and a half of coffee every morning, but my husband has quit drinking coffee. I find the effect on the bees very interesting. I have red studies about the positive effect for people, but I never considered bees. I know the bess colonies ar declining but I always thought it was due to insecticides, etc Thank you for sharing all this excellent information.