Since June 2011, a widely circulating e-mail from the US Institute of Health Sciences has been claiming that the humble lemon is "a miraculous product that kills cancer cells. It is 10,000 times stronger than chemotherapy." On its web-site, the Institute says it's devoted to "researching . . . advances in modern under-ground medicine", but there's no article on the cancer-fighting properties of lemons and absolutely nothing to substantiate the claim that lemons are better than chemotherapy. The e-mail suggests that lemons can be kept frozen in your freezer and grated onto your food-whether savoury or dessert-every day.
Is there any scientific evidence for the seemingly extravagant claims? Well, actually there is. A 2003 study investigated the tolerability and effect of modified citrus pectin (MCP)-available on the net as Pecta-Sol(R)-in men with prostate cancer. The study endpoint was changes in their prostate-specific antigen (PSA) levels over time (Prostate Cancer Prostatic Dis, 2003; 6: 301-4). The results showed a significant increase in the time it took PSA levels to double, suggesting that MCP had a slowing effect on the cancer's growth.
MCP is a form of pectin-the gelatinous long-chain sugar used to set jams-altered so that it's more easily absorbed in the gut. This is because the natural form of pectin
in lemon peel cannot be taken up by the body, but is more like an indigestible soluble dietary fibre. MCP also has a lower molecular weight compared with regular citrus pectin, and is rich in sugar (galactose) residues that are easily processed by the digestive system and absorbed into the bloodstream because it's in the correct molecular-weight range. In short, MCP has been chemically altered by pH and temperatures that break its long branching sugar chains into shorter lengths of soluble fibre.
There's also been a lab study of limonoids, the chemicals in lemon peel that give it that bitter taste. This research demonstrated that, at high levels, limonoids can slow cancer-cell growth and induce 'apoptosis', or natural cell suicide (J Nutr, 2005; 135: 870-7).
From the Greek word referring to the autumnal 'dropping of petals and leaves', apoptosis is the term used for the process of programmed cell death usually found in multicellular organisms. Inhibition of apop-tosis leads to various cancers where a galac-tose-specific lectin-a protein that binds to that particular sugar-called 'galectin-3' (Gal-3) is produced. This molecule has anti-apoptotic actions. The vast majority of the currently used anti-tumour drugs are attempting to induce tumour-cell apoptosis-and Gal-3 blocks their cell-killing efforts.
In 2009, a study showed that MCP is a natural Gal-3 inhibitor (Carbohydr Res, 2009; 344: 1788-91). This means that MCP can dramatically change the sensitivity of cancer cells to chemotherapy drugs by suppressing the anti-apoptotic effects of Gal-3. In fact, the results also strongly suggest that the simple addition of a nutritional supplement like Pecta-Sol to regimens for treating cancers that express Gal-3 should substantially boost the effect of the chemo. And it must be borne in mind that the MCP in Pecta-Sol is easily taken up by the digestive tract, whereas the natural pectin in lemon peel is not.
It's also worth pointing out that at least two recent studies have shown that, in addition to enhancing apoptosis by cytotoxic chemo drugs, MCP in itself appears to induce cancer-cell death (Neoplasia, 2009; 11: 901-9; Proc Natl Acad Sci U S A, 2011; 108: 20225-30).
In one of these studies, the ability of several forms of citrus pectin to induce apoptosis in human prostate cancer cells was investigated. The authors reported that fractionated pectin powder (made by Thorne Research and available online) was around 40 times more effective at killing prostate cancer cells than chemo alone.
On the other hand, natural citrus pectin and Pecta-Sol displayed little or no apoptotic activity. Also, heat treatment (rather than freezing) of natural citrus pectin led to significantly higher levels of cancer-cell death that were comparable to those with fractionated pectin powder.
Given that these findings have been in the public domain for some time, it rather begs the question of why the addition of an appropriate lemon-derived nutritional supplement is not routinely administered together with chemotherapy for breast and prostate cancers-not to mention all the other tumours and malignancies that express Gal-3.
WDDTY November 2012 vol 23 no 8