Which citrus fruits are likely to mess with your medication?

by Jennifer Bowden / 14 April, 2018

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Better to be safe than sorry when considering which citrus fruit plays havoc with medication.

QUESTIONI planted a seville orange tree to make marmalade and was sad to read I wouldn’t be able to eat the spread because it would react badly with my medication. I also have an ugli tree and wondered if its fruit is considered safe?

ANSWERThe troublesome compounds in citrus fruit, linked to the so-called grapefruit-juice effect, are furanocoumarins (FCs), which are produced as a defence against insects and other pathogens. FCs are good news for the plants but bad news for grapefruit lovers who take particular drugs.

Fred Gmitter, a horticultural scientist at the University of Florida’s citrus research and education centre, has studied FCs in citrus species and has developed a low-FC grapefruit hybrid known as UF 914. Although Gmitter hasn’t tested ugli fruit and can’t give a definitive answer, he notes that “ugli is a pummelo-mandarin hybrid and, as such, potentially produces FCs”.

Environmental conditions affect a fruit’s FC level, and a plant’s ancestral lineage also plays a big part. All citrus fruits come from four ancestral species: pummelo, citron, papeda and mandarin. The first three produce high levels of FCs, but mandarins have barely any.

French researchers subjected 61 citrus types to FC analysis and recorded widely varying concentrations. Their results, published in 2015 in the journal PLOS One, showed the lowest levels in sweet and acidic mandarins and most of their hybrids, which include sweet oranges, along with ichang papeda and two hybrids known as yuzu and mountain.

In contrast, pummelos, citrons and papedas, which have the highest levels of coumarins and furanocoumarins, produce hybrids that are also rich in FCs. The true grapefruit – a sweet orange and pummelo hybrid – predictably has high FC levels in line with that of its ancestral pummelo parent.

Without testing ugli fruit, it’s impossible to know their FC level, but as a pummelo-mandarin hybrid, it could be considerable.

QUESTIONYour recent column failed to mention that grapefruit from Florida and Israel and sold throughout much of the world are not the same as varieties such as golden special or wheeny grown in Kiwi backyards. Not for nothing are the local varieties called poorman orange. Does this mean our variants have lower FC levels than grapefruit grown in hotter climates?

ANSWERAlthough golden special and wheeny fruit are similar to grapefruit, citrus-breeding experts such as Gmitter contend that they are a form of pummelo hybrid, not “true” grapefruit.

Says Gmitter: “Florida grapefruit are ‘true’ [grapefruit], and some, but not all, Israeli grapefruit are as well. The same varieties of fruit from Israel, California and Florida were tested and the Israeli fruit contained the highest level of FCs, followed by California and then Florida.” In other words, grapefruit from the hottest region – Florida – had fewer FCs than those grown in cooler areas.

In New Zealand, golden special, which derives from morrison seedless, is the most commonly sold winter “grapefruit” variety, with a smaller volume of cutler’s red.

“We also market a small volume of star ruby grapefruit in January and February,” says David Stevenson, grapefruit manager for Gisborne-based First Fresh New Zealand.

Star ruby is a true grapefruit, whereas golden special is an improved version of the original poorman orange traditionally found in many New Zealand backyards. So the most common grapefruit in our shops are not “true” grapefruit.

But are they lower in FCs? In 2000, University of Otago researchers investigated levels of the compounds in fruit labelled “New Zealand grapefruit”, along with rio red, Dole and Sunkist varieties imported from the US.

All the fruit, bought from a Dunedin supermarket, contained FCs, although there were big variations between batches. Unfortunately, there’s no data confirming what variety of local fruit was tested.

On the basis that the poorman orange is probably a pummelo hybrid, like the ugli fruit, it seems safe to say it, too, will have an appreciable concentration of FCs.

This article was first published in the March 24, 2018 issue of the New Zealand Listener.

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