Professor Margaret Rayman, BSc, DPhil, a renowned selenium researcher at the University of Surrey in the UK, told NutraIngredients-USA that she’d also advise marketers and formulators to pull back on the doses to daily servings of 100 micrograms.
There is still a need for supplementation, she said, but only in regions where food levels are low, partly due to soil levels, and the US is not one of those places. Mean dietary selenium intakes in the US range from 93 micrograms in women to 134 micrograms in men, compared to only 40 micrograms per day in Europe (the RDA for US adults is 55 micrograms per day).
“The implications are clear,” she writes in an extensive review in The Lancet (2012, Vol. 379, pp. 1256-68), “people whose serum or plasma selenium concentration is already 122 microgams per liter or higher – a large proportion of the US population – should not supplement with selenium.
“The crucial factor that needs to be emphasized is the inextricable U-shaped link with selenium status: additional selenium intake (eg, from food fortification or supplements) may well benefit people with low status. However, people of adequate or high status could be affected adversely and should not take selenium supplements.”
SELECT
Selenium is an essential micronutrient, and is considered to be an antioxidant. The mineral is included in 25 selenoproteins in the body, with diverse roles including immune support, thyroid function and healthy sperm. The issue for selenium, as for other nutrients, is that you can get too much of a good thing.
Data from prospective studies have reported potential risk reductions for a number of cancers for selenium, and it is the only mineral that qualifies for a Food and Drug Administration (FDA)-approved qualified health claim for general cancer reduction incidence.
Clinical trials, however, have been scarce and the results disappointing. The most notable is the Selenium and Vitamin E Cancer Prevention Trial (SELECT), which was a clinical trial funded primarily by the US National Cancer Institute (NCI) and included over 35,000 men aged 50 and older in the US, Puerto Rico, and Canada.
The trial was ended prematurely when no effects on prostate cancer were observed. However, subsequent data analysis revealed a potential increased risk of prostate cancer in men taking vitamin E only. A small and non-significant increase in the risk of prostate cancer in the selenium only group was also reported, although that could be due to chance, according to the NCI.
Baseline data for the participants showed levels of 122-151 micrograms per liter, which would have already put them at the upward part of the U-curve for increasing risk, and then the participants received supplements.
“Doing SELECT in the US was a foolish thing right from the start,” said Prof Rayman. “It was already known from a previous trial and from the literature that you shouldn’t be giving people selenium supplements unless their levels are relatively low to start with.”
The market for selenium products reportedly started to lose steam following of the un-blinding of the SELECT cancer trial (although suppliers have said that sales have been holding steady in recent years). SELECT was also a death knell for a lot of selenium research.
“SELECT meant that you could no longer apply for any cancer work,” said Prof Rayman. “It’s extremely difficult to do a selenium-cancer study now, even in low selenium areas.”
U-shaped curve
While financial support for selenium studies has dried up, it isn’t a selenium research desert just yet. For example, researchers at the University of Otago in New Zealand have examined the potential impact of the trace mineral on depressive symptoms, and also observed a U-shaped effect. Data published in the Journal of Nutrition (2015, Vol. 145, pp. 59-65): Optimal levels of selenium in the range of 82 and 85 micrograms per liter were associated with reduced risk of depressive symptomatology, which was linked to when glutathione peroxidase is maximal. (Prof Rayman points out, however, that these levels are actually a bit lower than the concentration needed for maximum plasma GPx activity.)
A Swedish team led by Professor Urban Alehagen at Linköping University is also doing a lot of research combining selenium (200 micrograms per day, SelenoPrecise, Pharma Nord) with co-enzyme Q10 (200 milligrams per day, Bio-Quinon, Pharma Nord) for a range of end points, from cardiovascular mortality to quality of life. The results have shown significant benefits of the supplements, but again you have to consider the baseline levels of the participants was quite low (the mean plasma selenium was about 67 micrograms per liter).
China
As for Prof Rayman, she said she is now more focused on iodine as financial support for selenium studies declined. She has become involved in selenium research in China, where you can find areas with selenium levels lower even than those observed in the UK, she said. (She was appointed visiting professor at the First Affiliated Hospital Xi’an Jiaotong University School of Medicine, Xi’an, China in 2014.)
“In the Shaanxi province there are areas of high and low selenium and you have a very different prevalence of thyroid disease,” she said. The work was published in the Journal of Clinical Endocrinology & Metabolism (2015, Vol. 100, pp. 4037-47) and concluded: “Low selenium status is associated with increased risk of thyroid disease. Increased selenium intake may reduce the risk in areas of low selenium intake that exist not only in China but also in many other parts of the world.”
“I’d like to do an intervention there,” said Prof Rayman. “There are also parts of Europe where selenium status is really low, like in Poland and the Czech Republic, and selenium status is still an issue.”
“There will be countries where selenium supplementation is appropriate, and some countries where it’s irresponsible to do it,” she said.
So what is her advice for the industry? “What I’d say is be careful where you market and don’t have high dose tablets.”