Honey of a Threat
Janet Raloff
An all-natural, organic food, honey has a benign—if not wholesome—image. Many
people consider it a superior alternative to table sugar and corn syrup—two primary
sweeteners in the U.S diet.
However, honey has the potential to carry some very disturbing plant poisons to the
dinner table, an international trio of scientists reports. The World Health Organization has
already identified these toxins—pyrrolizidine alkaloids—as a serious human health
threat. In Europe, the toxins are coming under regulation, but only where they occur in
herbal medicines.
Honeys can be more potent sources of these
chemicals, John A. Edgar, a consulting
toxicologist from Melbourne, Australia,
and his colleagues note in an upcoming
issue of the Journal of Agricultural and
Food Chemistry. Moreover, they argue,
because honey aficionados sometimes
down large quantities of the syrup daily, the
potential for unwitting poisoning among
this segment of the population might be
high.
Though attractive to bees, borage may lace
its flowers’ nectar with toxic chemicals that
"We don’t want people to stop buying
could then show up in honey.
honey," Edgar emphasizes. However, his
James N. Roitman, USDA-ARS
team argues, if these toxins warrant
regulation in herbal medicines, they probably should at least be monitored in foods that,
like honey, might be eaten by infants, children, and the elderly—populations believed
most vulnerable to pyrrolizidine-alkaloid toxicity.
Newborn fatality linked to Mom’s tea
The idea that these populations are selectively vulnerable to pyrrolizidine alkaloids stems
from findings like the case reported in the March 1988 Journal of Pediatrics. Swiss
physicians described a baby born with jaundice, a massively enlarged liver, and other
problems. About 1 month later, the baby died.
Though the infant had experienced liver failure, her doctors were stumped as to why. The
newborn didn’t have hepatitis or any other common liver-damaging diseases.
The first clue to suggest poisoning came at the autopsy, which showed massive blockage
of vessels draining blood from the liver, noted Michel Roulet of the University of
Lausanne and his colleagues. Upon questioning, the mother reported that she had drunk
an herbal tea throughout her pregnancy. She made the tea from dried leaves purchased at
her neighborhood pharmacy, where the nostrum is sold as a phlegm-inhibiting cough
suppressant. Chemical analyses of this product showed it to be a rich source of
senecionine, a pyrrolizidine alkaloid (PA).
The baby’s condition, known as hepatic veno-occlusive disease, is a hallmark of PA
poisoning. In some cases, the alkaloids may also cause cirrhosis of the liver. "Normal
detoxification processes in the liver actually activate PAs," Edgar explains, turning these
chemicals into potent poisons. Not surprisingly, the liver then becomes their primary
victim.
While fatal to the infant, the tea had no noticeable effect on the mother.
Source in many flowers
Some 3 percent of flowering species make PAs, according to the upcoming Journal of
Agricultural and Food Chemistry paper. Many of those have a reputation as weeds—such
as Paterson’s curse (Echium plantigineum), tansy ragwort (Senecio jacobaea), and
Chromolaena. A few are plants distributed internationally by nurseries and home-garden
centers.
The Swiss researchers, in contacting the
manufacturer of the herbal tea responsible
for the baby’s poisoning, learned that it
contained leaves from 10 plants—including
Tussilago farfara. This PA-rich plant—
known commonly as coltsfoot or
coughwort—constituted some 9 percent of
the herbal preparation.
Several other PA-producing herb-garden
plants may be plucked for use in salads or
Comfrey, formerly a common herbal
home medicines. These include comfrey
(Symphytum officinale), Russian comfrey remedy, is gaining notoriety for the
potentially high concentrations of toxins that
(Symphytum X. uplandicum; formerly S.
may develop within various parts of the
pergrinum), and borage (Borago
officinalis). The first two have a history of plant, especially its roots. Several European
countries now prohibit—or are considering
folk use as emollients, sedatives,
laws that would ban—internal use of herbal
astringents, wound-healing agents, and
drugs containing comfrey.
expectorants. Borage is traditionally
recommended for soothing abraded mucus Russell J. Molyneux, USDA-ARS
membranes, as a diuretic, and as a stimulant. Borage oil also is a rich source of an omega3 fat, which some studies suggest can fight inflammation.
A few books on herbal medicine offer stern warnings of the risks posed by ingestion or
topical use of PA-containing plants. For instance, Steven B. Karch’s Consumer Guide to
Herbal Medicine concludes this about comfrey: "The danger of PA exposure has been
very clearly demonstrated. Occasional use of a tea made from second growth leaves is
unlikely to do much harm, but consumers who buy herbal remedies have no way to be
certain which part of the plant they are buying." Since liver failure "is not a nice thing,"
Karch argues that "[t]aking comfrey . . . would hardly seem to be worth the risk."
Other tomes downplay concern about certain PA-producing plants. For instance, 7 years
after the Journal of Pediatrics paper on the Swiss poisoning from coltsfoot, the Herb
Society of America Encyclopedia of Herbs and Their Uses pronounced: "The herb
contains PAs, which have not proved toxic at low dosages in tests." This book offered no
warning of possible fetal risks and concluded that "there is no suggestion that T. farfara
should be banned for internal use."
Who’s a consumer to believe?
The World Health Organization, for one, Edgar says. After reviewing a huge body of
data, it concluded in a 1988 report that PA-tainted foods have triggered several poisoning
outbreaks—with high mortality. Moreover, it reported that PAs produce delayed,
progressive, chronic effects following even brief, low-level exposures. Finally, the WHO
noted that PAs cause mutations, can damage genes, and have triggered cancer in rats.
In 1992, the German government responded by setting strict limits on the concentrations
of PAs it would tolerate in herbal medicines. Regulations limit the alkaloid’s
concentrations to 1 microgram per daily dose of a drug in medicines that will be ingested.
Such products are to be used for no more than 6 weeks annually—and never by children
or pregnant women. For herbal preparations that might be consumed regularly, Germany
cut tolerable PA concentrations lower still, to 0.1 microgram per daily dose.
Various countries in the European Union have adopted or are now considering adoption
of similar limits, Edgar notes—and the EU has just created a committee to investigate the
development of such limits to be applied consistently throughout its member nations.
What about foods?
PA regulations have focused on herbal medicines. The irony, Edgar says, is that studies
have demonstrated that the same troublesome poisons can turn up in foods, such as
honey, at concentrations that exceed Germany’s regulated limits for herbal drugs.
For instance, the scientists note one study that found PA concentrations of roughly 4
micrograms per gram in a honey. This amount is not detectable by taste. Bees appeared to
have picked up the toxins when they visited tansy ragwort, a weed common throughout
much of the world, including the western United States.
Considering that some infants consume up to 32 g of honey per day and adults up to 90 g
daily, there is potential for high PA intake.
Identifying the general source of the nectar collected by bees wouldn’t necessarily flag
PA contamination. Edgar says that a honey might be labeled as coming from a particular
type of flower, such as clover, when that flower represents only 45 percent of nectar the
bees collected. However, even if 95 percent of the nectar came from the labeled source,
the honey still might carry traces of PAs.
Just a few of the bees in a hive going to a tansy ragwort, Edgar says—“we’re talking one
bee in a thousand”—could spike the resulting honey with PA concentrations that would
be banned under German law for herbal drugs. Since apiculturists don’t tether their bees,
there’s no way to keep rogue buzzers from harvesting nectar at any flower nearby.
And PA-producing weeds can often be found in and amongst crop plants, especially in
developing countries. Indeed, Edgar notes, many Asian mass-poisoning outbreaks
occurred when local crops were harvested together with adjacent PA-rich weeds, which
tainted the batches of grain sent on to market.
A plea for research
At present, no one knows how big or small a threat the PAs in honeys pose. The reason,
Edgar laments, is that nobody has investigated the issue on more than a cursory,
academic level.
Perhaps a half dozen studies have detected PAs in honey, he notes—but only because PA
researchers had reason to believe bees had visited plants producing the alkaloids.
Contributing to his concern about the issue are several reports in publications aimed at
beekeepers about the potential advantages of encouraging their colonies to harvest nectar
from borage, a plant increasingly grown as a source of a reputedly healthy vegetable oil
that has a specialized market.
For instance, in a 1997 article in The Beekeepers Quarterly, a British publication, Lester
Quayle notes that “borage cultivation has been developed in England and the expertise
exported to the world.” He goes on to note that “Although there seems to be no
recommended ratio of hives per acre, [one beekeeper] feels that ‘the more the merrier.’”
A beekeeper himself, Quayle notes that borage honey “is startlingly clear,. . . slow to
crystallize and ideal for cut comb and chunk honey.” He adds that the health benefits
attributable to borage oil might help to build a big following for the plant’s honey.
A 1999 report in Bee World notes that borage is so attractive to bees that it is commonly
grown by people to invite bees into their garden. With this intentional nectar harvesting
from borage, Edgar says, one has to worry about potential for PA contamination of that
honey. Yet, to date, there doesn’t appear to have been any investigation of PAs in this
nectar or the honey that results.
Edgar’s team argues that researchers should look into various types of honey. All three
authors of the new Journal of Agricultural and Food Chemistry review have spent parts
of their careers investigating human PA-poisoning incidents. Two of the authors, Edgar
and Russell J. Molyneux of the Agriculture Department’s Western Regional Research
Center in Albany, Calif., have also researched the toxins’ effects on livestock and foods
made from tainted animals.
They teamed up for the new review paper, Edgar told Science News Online, in the hope
that it would “prompt more monitoring and more awareness of the potential problem.
Personally, ”I’d also like to see this issue more widely debated in the food-safety riskassessment community.”
PAs are only one of many potent trace toxicants lacing the food supply. However, as with
aflatoxin on peanuts and fumonisins on corn flakes, these near ubiquitous poisons can be
kept to very low concentrations by routine monitoring—and a culling of any highly
contaminated batches. Edgar says that there’s even the prospect of one day deliberately
breeding lower production of PAs among plants destined for our gardens.
References:
Bown, D. 1995. Herb Society of America Encyclopedia of Herbs and Their Uses. New
York: Dorling Kindersley. See http://www.sciencenewsbooks.org/newenofheran.html.
Edgar, J.A., et al. In press. Honey from plants containing pyrrolizidine alkaloids : A
potential health threat. Journal of Agricultural and Food Chemistry.
Karch, S.B. 1999. The Consumer's Guide to Herbal Medicine. Hauppauge, N.Y.:
Advanced Research Press.
Osborne, J.L. 1999. Borage. Bee World. 80(No. 1):33. See http://www.cf.ac.uk/ibra/bwjourn.shtml.
Quayle, L. 1997. Honeybee forage. Beekeepers Quarterly. 49:22. See
http://www.beedata.com/bbq.htm.
Roulet, M., et al. 1988. Hepatic veno-occlusive disease in newborn infant of a woman
drinking herbal tea. Journal of Pediatrics 112 (March):433-436.
Further Readings:
Raloff, J. 2002. Honey may pose hidden toxic risk. Science News 161(May 18):317.
Available to subscribers at http://www.sciencenews.org/20020518/note10.asp.
______. 1998. The color or honey. Science News 154(Sept. 12):170-171. Available at
http://www.sciencenews.org/sn_arc98/9_12_98/Bob1.htm.
______. 1997. Sphinx of fats. Science News 151(May 31):342-343.
______. 1992. Liver cancer: Homing in on the risks. Science News 142(Nov. 7):308.
Schatzki, T.F., and W.F. Haddon. In press. Rapid, non-destructive selection of peanuts
for high aflatoxin content by soaking and tandem mass spectrometry. Journal of
Agricultural and Food Chemistry.
Wu, C. 1997. Chemical buzz. Science News 151(May 24):324-325. Available at
http://www.sciencenews.org/sn_arc97/5_24_97/bob1.htm.
Sources:
John A. Edgar
c/o CSIRO Livestock Industries
PB 24
Geelong
Victoria 3220
Australia