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I used Google to try to figure out what kind of mixture honey has with hot water, and I found several Ayurvedic sources claiming that honey in hot water is toxic.

For example:

What I would like to know is how does heating honey make it toxic?

Is there something that happens at the molecular level that changes the chemical properties of honey when it is heated? If so, are these chemicals harmful, as claimed?

Are there any other reasons other than heating that may make honey toxic?

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    $\begingroup$ Could you provide references to your claim? $\endgroup$ – Memming Dec 28 '15 at 20:20
  • $\begingroup$ I assume you are talking about sites like markbunn.com.au/honey_never_in_hot_water or mockingbirdmeadows.com/2013/11/19/… ? Basically claiming that heating honey will kill us all (well, maybe not kill, just make us very sick)? $\endgroup$ – YviDe Dec 29 '15 at 1:00
  • $\begingroup$ @YviDe, I added some information from an Ayurvedic Research journal that addresses those issues. There concern is an increase in HMF, but HMF is a breakdown product of hexoses, and will be found in anything that contained fructose and glucose that was heated, not just honey. However HMF has not been found to be correlated to any illnesses in humans, so the significance of the find is questionable. $\endgroup$ – AMR Dec 29 '15 at 1:56
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    $\begingroup$ I am voting to reopen this question. In answering the question, I realized that there was a biochemical process at work when honey is heated that transforms hexoses into hydroxymethyl furfuraldehyde. As such, there the question and its answer would be relevant from a biochemistry. I have edited the question to bring it more in line with a question on topic for Biology S.E while trying to maintain the question the OP was trying to find out which is what makes heated honey toxic and is honey in tea safe to drink. $\endgroup$ – AMR Dec 30 '15 at 1:01
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    $\begingroup$ Nice edits @AMR $\endgroup$ – rg255 Dec 30 '15 at 6:57
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Heated Honey and HMF

In this paper, Studies on the physicochemical characteristics of heated honey, honey mixed with ghee and their food consumption pattern by rats, by Annapoorani, et.al.;
International Quarterly Journal of Research in Ayurveda, 2010 Apr-Jun; 31(2): 141–146.
doi: 10.4103/0974-8520.72363, the report finds a statistically significant increase in the compound hydroxymethyl furfuraldehyde (HMF).

The compound was studied by the National Toxicology Program of the U.S. Department of Health and Human Services in Mice and Rats and the results were published in a report dated June of 2010.

5-(Hydroxymethyl)-2-furfural is formed when reducing sugars such as fructose and sucrose are heated in the presence of amino acids. 5-(Hydroxymethyl)-2-furfural is ubiquitous in the human diet and occurs at concentrations greater than 1 g/kg in dried fruits, caramel products, certain types of fruit juices, and up to 6.2 g/kg in instant coffee. 5-(Hydroxymethyl)-2-furfural also occurs naturally and has been identified in honey, apple juice, citrus juices, beer, brandy, milk, breakfast cereal, baked foods, tomato products, and home cooking of sugar and carbohydrates.

- NTP toxicology and carcinogenesis studies of 5-(Hydroxymethyl)-2-furfural (CAS No. 67-47-0) in F344/N rats and B6C3F1 mice (gavage studies).; Natl Toxicol Program Tech Rep Ser. 2010 Jun;(554):7-13, 15-9, 21-31 passim.

HMF is a breakdown product of Fructose, Glucose, and Cellulose (hexoses) and is found in many products, especially high fructose corn syrup, after heating, and is excreted in the urine. However, it has not been correlated to any diseases in humans (4). In the NTF toxicology and carcinogenesis studies, the conclusions were that

under the conditions of these 2-year gavage studies, there was no evidence of carcinogenic activity of 5-(hydroxymethyl)-2-furfural in male or female F344/N rats administered 188, 375, or 750 mg/kg. There was no evidence of carcinogenic activity of 5-(hydroxymethyl)-2-furfural in male B6C3F1 mice administered 188 or 375 mg/kg. There was some evidence of carcinogenic activity of 5-(hydroxymethyl)-2-furfural in female B6C3F1 mice based on increased incidences of hepatocellular adenoma in the 188 and 375 mg/kg groups. Administration of 5-(hydroxymethyl)-2-furfural was associated with increased incidences of lesions of the olfactory and respiratory epithelium of the nose in male and female rats and mice.

- NTP toxicology and carcinogenesis studies of 5-(Hydroxymethyl)-2-furfural (CAS No. 67-47-0) in F344/N rats and B6C3F1 mice (gavage studies).; Natl Toxicol Program Tech Rep Ser. 2010 Jun;(554):7-13, 15-9, 21-31 passim.

As is shown in the NTP report and the other sources above, HMF is not only found in honey. It will be found in any product that contained sugar or high fructose corn syrup that has been heated, such as baked goods. The reason you are likely to encounter it in honey is foremost that honey is 70-80% reducing sugars (5) and also that bee keepers often supplement HFCS for actual flower nectar when there is not enough flower nectar available for the bees to use to produce honey.

Toxic Honey

One thing to note is that there are toxic forms of honey, just as there are poisonous mushrooms and edible mushrooms. Honey derived from rhododendrons can contain Grayanotoxin, however it is rarely fatal in humans. If you are buying your honey from a supermarket or a reputable keeper, then there is almost no chance that your honey will contain grayanotoxin.

Why is Honey Harmful to Infants?

The issue with honey is that it can contain Clostridium botulinum spores. If the spores germinate, the resulting bacteria release botulinum toxin.

Botulinum toxin, which is the cause of botulism, is a neurotoxin that causes dystonia, and can be lethal in minute doses (ng/kg doses).

For most adults, the risk of botulism from the spores found in honey is minute. The gut microbiome and immune system proteins such as defensins will prevent C. botulinum colonization, so even if the spores germinate, they will not grow to a critical mass to produce enough toxin to do harm and will be excreted.

This however is not the case for infants less than six months of age. Their microbiome is still developing and their immune system is not fully formed. Also, as they have less mass, it takes a lesser absolute amount of the toxin to cause illness and death.

C. botulinum spores are heat resistant, though they can be killed by boiling (7), which means that the internal temperature of the spore needs to reach >85°C for over 5 minutes. Pasteurized honey should already have had this treatment, however you will still see the warnings to not feed to infants less than six months to one year of age, as commercial heat pasteurization may not kill all of the spores (7).

So unless you are immunocompromised, have no gut microbiome, are an infant less than six months of age, or your boiled water does not stay at a temperature greater than >85°C for longer than 5 minutes, and are using raw honey, then you shouldn't be at too much risk.

Edit

Information has been reorganized to better reflect edit to question.

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