There has been much interest in the role of selenium in recent years. As intakes
have drifted downwards in Europe, concern has been expressed that marginal
deficiencies may be putting us at greater risk of developing chronic diseases like
cancer and heart disease. But is this the case and what should be done about it?
Vital role in the body
In the body, selenium is incorporated into a number of vital proteins called selenoproteins.
Twenty five selenoproteins have been identified so far, including i) peroxidases that have
important antiinflammatory properties and protect cell membranes from damage by free
radicals, ii) deiodinases involved in the production of active thyroid hormone and iii)
proteins involved in reproduction and DNA repair.
Sources of selenium
Selenium is found in soil and rocks, it accumulates in plants and this is how it enters the
food chain. Selenium is present in most foods, with nuts (especially Brazil nuts), fish and
seafood, offal (kidney, liver) and meat being very good sources. Cereals, vegetables and
other plant foods contain selenium, but the amount varies according to the soil they grow
in. European soil is relatively low in selenium, compared to areas in for example America, Canada and China.
Lower intakes
Selenium intakes in Northern Europe have generally dropped considerably over recent decades. In the 1970s intakes were
around 6070 μg per day whereas now intakes are estimated at only 30 μg for women and 40 μg per day for men
1
, which is
about half the current recommended amount.
2
It is believed that the reason may be a greater reliance on homegrown instead
of imported wheat from Canada and America, which contains up to 50 times more selenium than the European equivalent.
Interestingly Finland introduced selenium into fertiliser in the 1980s and levels have increased correspondingly (see table).
Weakened defences
Although selenium intakes are on the low side, obvious signs of deficiency are not seen in Europe. But suboptimal selenium
intakes may reduce the production of selenoproteins, which in turn might affect DNA repair, impair the immune and anti
inflammatory responses, and reduce protection against diseases like cancer and heart disease.
Selenium and cancer
The role of selenium in the development of cancer was reviewed extensively recently.
3
Although there are plausible
mechanisms by which selenoproteins could reduce the likelihood of developing cancer (for example by mopping up free
radicals that cause DNA damage), it was concluded that there was limited evidence that foods containing selenium protect
against the risk of any form of cancer, except for prostate cancer. Selenoproteins may lower prostate cancer risk because they
are involved in the production of testosterone, which is an important regulator of both normal and abnormal prostate growth.
Heart disease
A metaanalysis of thirteen observational studies examining the role of selenium in heart disease found a moderate inverse
relationship between markers of selenium status and the risk of heart disease. However, studies in selenium replete
populations find no evidence of cardiovascular protection and supplementation studies are largely inconclusive.
4
Safety margin
In Europe, the safe upper limit of selenium intake has been set at 300 μg/day for adults, gradually decreasing to 60 μg/day for
children aged 13 years.
2
Exceeding these levels may, in mild cases, cause skin lesions and loss of hair and nails, whereas
large longterm doses (over 900 μg/day) can result in neurological changes including numbness, convulsions and even
paralysis. Excessive selenium intake from food sources is very rare, but cases of toxicity have been reported in Swedish
children who accidentally overconsumed selenium tablets.
5
Moderate intakes are best
Although selenium intakes in Europe have fallen, they are still sufficient to prevent any obvious signs of deficiency and are
similar to many other areas of the world (see table).
1
Levels of selenoproteins appear to reach their maximal levels relatively
easily at normal dietary intakes and do not increase further with selenium supplementation.
3
This is in line with a recent review
on antioxidant supplements that attributed no clear benefits to consuming additional selenium from nonfood sources.
6
By
eating a varied diet, most people will get enough selenium from their food.
Selenium in the Diet
Geographic differences in the selenium intakes
References
1. FAO/WHO (2002). Human Vitamin and Mineral Requirements. Report of an expert consultation, Bangkok Thailand.
Chapter 15 Selenium. Available at:
http://www.fao.org/DOCREP/004/Y2809E/y2809e0l.htm#bm21.1
2. Scientific Committee on Food (2000) Opinion of the Scientific Committee on Food on the Tolerable Upper Intake Level of
Selenium. Available at:
http://ec.europa.eu/food/fs/sc/scf/out80g_en.pdf
3. WCRF/AICR (2007). Food, Nutrition, Physical Activity and the Prevention of Cancer – a Global Perspective. Washington
DC. Available at:
4. NavasAcien A, Bleys J & Guallar E (2008). Selenium intake and cardiovascular risk: what is new?. Current Opinions in
Lipidology 19:4349
5. Johansson L, Åkesson B and Alexander J (1997). Availability of selenium from soils in relation to human nutritional
requirements in Sweden – Is there a need for supplementation. Report. Swedish Environmental Protection Agency,
Stockholm, 104 pp.
6. Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C (2008). Antioxidant supplements for prevention of mortality
in healthy participants and patients with various diseases. Cochrane Database of Systematic Reviews 2008, Issue 2.
Art. No.: CD007176. DOI: 10.1002/14651858.CD007176.
(µg/day) of adults
1
Region or country
Selenium intake
(Mean ± standard error or range)
New Zealand, lowselenium area
11 ± 3
China, diseasefree area
13 ± 3
China, seleniferous area
1338
South Sweden
40 ± 4
Finland, before selenium in fertiliser 26
Finland, after selenium in fertiliser
56
Slovakia
27 ± 8
United Kingdom, 1974
60
United Kingdom, 1995
33
Italy
41
Germany
38 48
France
47
United States
80 ± 37
Canada
98 224
Venezuela
80 500
2
At the recent Food in Action conference organised in conjunction with EUFIC,
psychologist Dr Andrew Hill revealed a number of counterintuitive findings about
what makes adolescents obese. His findings shine an alternative light on the issue
and offer insight into new approaches to tackle this problem.
Unexpected finding
There are now a number of studies which have followed a large group of children through
adolescence over time. This makes it possible to examine what behaviors contribute to
subsequent obesity. Two such studies, the 1970 British Birth Cohort, and the US based EAT
(Eating Among Teens) and others like them, have discovered a risk factor for obesity that is not
only surprising, but the opposite of what you might expect – dieting.
1,2
Dieters more likely to develop obesity
Viner and Cole found that adolescents who were dieting to lose weight at age 16 were
significantly more likely to be obese at age 30 than nondieters.
1
NeumarkSztainer and
colleagues found that teenagers who reported to be dieting at the onset of the study period
were three times more likely to be obese after five years than their nondieting peers.
2
These
findings are equally true for boys and girls.
Type of diet makes no difference
The NeumarkSztainer study also examined whether the type of diets the adolescents followed made any difference. Dr Hill
highlighted that ‘healthy’ practices like the lowfat, wellbalanced diets rich in fruit and vegetables (i.e. the type that health
professionals would recommend) were as unsuccessful as ‘unhealthy’ weight loss behaviour such as fasting, missing meals,
extreme and faddy diets or self induced vomiting.
Does dieting lead to weight gain?
There are various possibilities as to why dieting may lead to obesity such as the deregulation of appetite, where hunger becomes
dissociated from actual eating, and dietary restraint, i.e. not eating to appetite/satiation, which can lead to binge eating. Both of
these factors leave the dieter vulnerable to overeating and hence weight gain. However, whatever happens once the child starts
dieting Dr Hill points out:
‘Dieting in adolescence is a proxy for difficulty in regulating food intake. These teenagers have recognised they have a weight problem,
responded by dieting, and broadly failed. Thus, dieting is not the cause but a response to being overweight’
Family influence
So why are these children struggling with their weight? Dr Hill explained that the literature consistently reveals that the most
powerful risk factor for weight problems in children and young adults is having overweight or obese parents. For example, the
Health Survey for England (2006) shows how the risk of obesity in children aged 215 years jumps sharply from almost zero to
about 15% if one, and up to 28% if both parents are overweight or obese.
3
Most likely, genetic and environmental factors combine
to bring about this increased risk.
Other risk factors
A recent study by Stice and colleagues recorded psychological profiles and behavioural practices in a group of 500 adolescent girls
and followed them for four years.
4
It was found that dietary restraint, radical weight control practices, like vomiting and appetite
suppressants, depressive symptoms and perceived parental obesity (but not highfat food consumption or exercise frequency)
predicted the onset of obesity. Apart from parental obesity and dieting practices, this study also highlights a link between
depression and obesity.
‘There is now a substantial body of evidence linking depression with the development of obesity’ added Dr Hill. ‘Some studies have tried to
unravel the underlying causes. Body dissatisfaction, perceived social isolation, the shame of being overweight and being teased and bullied
seem to be important mediators.’
The way forward
The evidence clearly shows that the development of obesity in young people is not simply about physical activity and energy
intake. It is undoubtedly a complex problem where there are a lot of (poorly understood) psychological vulnerabilities involved. So
what is the way forward? Dr Hill suggests:
‘Creating a public health environment encouraging weight control is not enough for our young people. We need tailored interventions, and if we
target anyone it should be families where both parents are obese or overweight. We need people on the ground who can provide individual
assistance to help these families overcome the barriers to their long term success in weight control.’
References
1. Viner RM and Cole TJ (2006). Who changes body mass between adolescence and adulthood? Factors predicting change
in BMI between 16 years and 30 years in the 1970 British Birth Cohort. International Journal of Obesity 30:13681374
2. NeumarkSztainer DR , Wall MM, Haines JI et al (2007). Shared risk and protective factors for overweight and
disordered eating in adolescents. American Journal of Preventive Medicine 33:359369
3. Health Survey for England 2006: CVD and risk factors adults, obesity and risk factors children (2008). Available at
http://www.ic.nhs.uk/statisticsanddatacollections/healthandlifestylesrelatedsurveys/health
surveyforengland/healthsurveyforengland2006:cvdandriskfactorsadultsobesityandrisk
Dieting and weight increase in adolescents
3
4. Stice E, Presnell K, Shaw H and Rohde P (2005). Psychological and behavioural risk factors for obesity onset in
adolescent girls: a prospective study. Journal of Consultant Clinical Psychology 73:195202
Conference proceedings available at:
http://www.focusbiz.co.uk/conferences/foodinaction/day2.htm
4
Some people believe that foods high in fat or sugar might be addictive, thereby
driving consumers to overeating and obesity. Does it mean that foods should be
regarded in the same way as alcohol or cigarettes? Or is it that people confuse
the terms “addiction”, “craving” and “eating disorders”?
Why do some people talk about “addiction” in the context of
food consumption?
Addiction is characterised by the compulsion to use a substance, uncontrolled
consumption, and the existence of withdrawal symptoms (such as anxiety and irritability)
when access to the substance is prevented. People suffering from eating disorders such as
‘binge eating’, bulimia nervosa and anorexia nervosa tend to display these symptoms,
suggesting similarities between how the body reacts to drug use and compulsive eating.
Common pathways in the brain are thought to be responsible for the sensation of pleasure
derived from food intake and drug use. For example, studies with laboratory rats have
shown that repeated, excessive intake of sugar can sensitise brain receptors to dopamine
(a substance produced in the brain when we experience pleasure) in a similar way to the
abuse of illicit drugs. Studies in people using brain neuroimaging techniques, which enable
imaging the structure and function of the brain, also indicate similarities between physiological responses to anticipation of
palatable food and that of drugs of abuse – for example, dopamine is released in the same brain areas.
The case against “food addiction”
Despite these commonalities between eating and drug use, the vast majority of cases classified as “food addiction” should not
be viewed as addictive behaviour. Eating is a complex behaviour involving many different hormones and systems in the body,
not just the pleasure/reward system. Recent research has shown some differences in the changes produced in several
neurotransmitters by drugs and the intense compulsion for food.
1
Besides, virtually every pleasure we encounter – beauty,
music, sex, even exercise is associated with surges of dopamine similar to those caused by a meal high in fat. But we call
these pleasures, not addictions, and academics have proposed alternative explanations.
The strong desire for a pleasurable food (such as chocolate) conflicts with the culturallyimposed need to restrict intake,
making the desire for the food more pronounced and to be interpreted as an addiction (e.g. "chocoholism"). It could also be
that in some individuals, there are differences in how the brain processes the eating stimuli that are similar to addictive stimuli,
resulting in stronger drives to consume different amounts or types of foods.
Food cravings and eating disorders
The term “food craving” is often more appropriate than “food addiction”. It is "an intense desire to consume a particular food
or food type that is difficult to resist." Actually, food cravings are common. Almost all women and most men experience some
sort of food craving at one point in their lives. The most often reported cravings are for chocolate (40% of women) or, more
generally, for foods high in fat and/or sugar or high in carbohydrates.
Food cravings are significant because they may play a role in excessive eating observed in binge eating, bulimia and obesity,
although the question remains open. Various theories exist to explain the relationship between food cravings and eating
disorders; depending on the authors, they emphasise physiological homeostasis, learning mechanisms involving sensory
aspects of food, or other psychological principles related to emotions. For example, it has been suggested that individuals
ingest carbohydrates in an effort to elevate mood – the underlying mechanism is an increase in brain serotonin (a substance
that plays an important role in the regulation of mood and appetite). Similarly, it has been suggested that psychoactive
substances in chocolate cause the craving, but research shows that sensory properties appear to be the most important
determinant of the desire for chocolate.
What does this mean for most people?
Even if the term ‘addiction’ is inappropriate, it focuses the mind on an important aspect of healthy eating behaviour – the ability
to maintain control over one’s diet.
While exercise and healthy eating habits are the wellproven routes to good health in nearly all people, current research from
neuroscience and new findings that the most potent brain circuit known to control food intake also regulates peripheral lipid
metabolism may help health professionals to better support people who find their eating habits at odds with their intentions.
2
References
1. Fallon S et al (2007). Food rewardinduced neurotransmitter changes in cognitive brain regions. Neurochemical
Research 32: 17721782
2. Nogueiras R et al (2007). The central melanocortin system directly controls peripheral lipid metabolism. The Journal of
Clinical Investigation doi:10.1172/JCI31743
3. Rada P, Avena NM and Hoebel BG (2005). Daily bingeing on sugar repeatedly releases dopamine in the accumbens
shell. Neuroscience. 134:73744.
4. Rogers PJ and Smit HJ (2000). Food Craving and Food "Addiction". A Critical Review of the Evidence From a
Biopsychosocial Perspective. Pharmacology Biochemistry and Behaviour. 66:314.
5. Yanovski S (2003). Symposium: Sugar and FatFrom Genes to Culture. Sugar and Fat: Cravings and Aversions. Journal
of Nutrition 133:835S837S.
Food addiction or food craving?
5
The classical food risk analysis model, developed in the 1990s, breaks the risk
analysis process into three stages: risk assessment, risk management, and risk
communication. But some scientists believe that this model – and practices
associated with it – may not be addressing consumers’ concerns on challenging
food safety issues.
SAFE FOODS project
SAFE FOODS, an EUfunded Integrated Project (running from April 2004 to June 2008) has
developed a more holistic approach to food safety, responding directly to consumers’
concerns. The project has brought together 37 consortium partners, including leading
European scientific food research institutes, organisations, universities and partners from
South Africa and China.
SAFE FOODS launched an exploration to identify consumers’ food safety concerns,
prioritise these concerns efficiently, and find out how best to use currently available tools
(e.g. technology, surveys, regulatory processes) to respond better to consumer needs.
SAFE FOODS took a multidisciplinary view of how all aspects of the risk analysis process could potentially evolve, from
scientific risk assessment to communicating with consumers. A key finding was that leveraging existing national knowledge to
create a panEuropean or global view could optimise this process.
Making national intelligence internationally accessible
SAFE FOODS developed an online database of 400 food safety experts from 260 organisations in over 35 countries.
Governments and authorities will be able to use this technology to swiftly identify relevant experts.
A fully operational webbased transfer point where registered members can exchange national intelligence on emerging issues
and food safety hazards was also created by the SAFE FOODS team. This technology accelerates hazard identification by
bringing together overviews of the more than 300 national and EUinitiatives dealing with food safety issues. Although the
database is still in its infancy, several national and European organisations have already expressed their interest in becoming
users.
Apfelstrudel = tarte aux pommes?
Countries collect data on food consumption and food contaminants and toxins, but the ability to compare different countries’
data is generally limited because food is coded and collected differently in each country. SAFE FOODS overcame this challenge
by using the Codex harmonised coding method to recode food products (e.g. apple pie) in five countries as raw agricultural
commodities (e.g. apples, flour, sugar, butter). Recoding the national data allowed SAFE FOODS to perform a simulation, which
revealed whether different consumption habits or monitoring practices explained the differences between national data.
Stateoftheart technology
SAFE FOODS explored ways to integrate stateoftheart technologies to maximize the use of available data. The project
analysed the composition of potatoes and maize using an innovative “omics” technique. This technology can allow scientists to
perform unprecedented analyses of crop composition by measuring thousands of parameters at once (including genes,
proteins and metabolites). Scientists could thus determine whether inserting a new gene in a maize kernel unintentionally
changes its composition, and risk managers could understand how the crop’s cultivation process changes the nutritional value
of the food (e.g. nanotechnology, GM, organic).
Improving risk communication
SAFE FOODS conducted consumer research on how risk communication could be optimised. Observations were that risk
information should be tailored to consumers’ needs and that uncertainty and variability must be addressed by coordinating
information on food risks. The project thus recommends that communication efforts on food risk management consider
regulatory priorities, preventative measures, enforcement actions and the expertise of food risk managers.
Modernising the food risk analysis model
Many practitioners admit that the classical risk analysis model is still applicable for most routine decisions on noncontroversial
issues. SAFE FOODS finds that controversial topics, however, should be assessed in a wider context than is currently the case.
SAFE FOODS makes bestpractice recommendations, which amend the classical risk analysis model to optimise the risk
analysis process.
Some recommendations, such as the inclusion of stakeholders in risk analysis, are already partially incorporated into the
regulatory process. The European Commission has established the Advisory Group on the Food Chain and the Animal and Plant
Health and the Stakeholder Dialogue Group. The European Food Safety Authority has created a Consultative Stakeholder
Platform.
Areas for further exploration remain, such as developing technical guidance on how and when to use omics technology and
training programs on how to use the results from these analyses to make decisions.
Although the SAFE FOODS project may be nearly over, development of its thoughtprovoking methodology is not.
EU SAFE FOODS project questions the current approach to food risk analysis
6