CARDIOVASCULAR JOURNAL OF AFRICA • Vol 22, No 6, November/December 2011
328
AFRICA
have higher DHA to EPA ratios.
23
According to Kris-Etherton
et al.,
16
the majority of commercially available n-3 fatty acid
supplements in the United States provide 180 mg EPA and 120
mg DHA per capsule, representing a ratio of 1.5:1 EPA to DHA.
EPA and DHA have different effects on various health aspects
and under certain conditions it seems that a higher DHA to EPA
ratio is preferable.
In the brain, DHA is the main n-3 polyunsaturated fatty
acid,
24
and the importance of DHA in neural and visual develop-
ment and function, especially during pregnancy, lactation and
infancy,
25,26
is well documented. Additionally, deficits in DHA
appear to contribute to inflammatory signalling, apoptosis and
neuronal dysfunction in the progression of Alzheimer’s disease
(AD), a common and progressive age-related neurological disor-
der unique to structures and processes of the human brain.
27
With regard to cell function, Gorjão
et al.
22
reported that some
studies have shown that EPA and DHA have diverse effects on
cell functions such as leukocyte functions. EPA and DHA also
modulate the expression of genes in lymphocytes differently, and
affect the activation of intracellular signalling pathways involved
with lymphocyte proliferation in a different way, therefore neces-
sitating different EPA to DHA ratios to ensure optimal function.
Mori and Woodman
28
compiled a review on the independ-
ent effects of EPA and DHA on risk factors for cardiovascular
disease in humans. From their report, it seems that EPA and
DHA have diverse haemodynamic and anti-atherogenic effects.
According to Mori and Woodman,
28
both EPA and DHA are
effective in reducing serum triglyceride levels but only DHA has
the ability to increase high-density lipoprotein cholesterol (HDL-
C). DHA also increases low-density lipoprotein (LDL) particle
size, a potential anti-atherogenic effect. Neither EPA nor DHA
show any effects on total cholesterol, while it appears that DHA
is more effective in reducing blood pressure and heart rate when
compared to EPA.
However, most clinical data available on the cardiovascular
effects of n-3 fatty acids used a combination of EPA
+
DHA
supplementation. Future research studies should therefore assess
the individual effects of EPA and DHA in a variety of clinical
settings and target populations, before decisions can be made on
specific ratios of EPA to DHA in supplements and food fortified
with either EPA or DHA.
Conjugated dienes (CDs) contain two or more double bonds
and are formed during the oxidation process of unsaturated fatty
acids to ensure a more stable radical.
30
CDs are used to deter-
mine primary oxidation products and therefore provide an early
indication of the levels of lipid oxidation.
31
Although primary
oxidation products such as CDs have no colour or flavour of their
own, they can readily be decomposed to secondary products such
as aldehydes, ketones and alcohols. These secondary oxidation
products have distinctive flavours and contribute to the offensive
taste of decomposed seafood and marine oils.
31
Considering the CD content of commercially available South
African n-3 fatty acid supplements, it seems that the majority
contain high amounts of primary oxidation products. No clear
relationship could be established between the expiry dates and
the CD content of the n-3 supplements. These results therefore
suggest that a considerable variation exists in the quality of the
fish oil present in n-3 capsules in South Africa. This indicates
that the oils present in many of the supplements are in the first
stages of rancidity and hence negatively influence the quality of
the product that consumers buy.
An additional health concern related to fish and fish oil
supplements is that some species of fish may contain consider-
able levels of heavy metals such as methyl mercury.
8
Methyl
mercury may be present at low levels in fresh waters and oceans
but tends to concentrate in the aquatic food chain such that levels
are generally highest in older, larger, predatory fish and marine
mammals. Fish and seafood are a major source of human expo-
sure to methyl mercury.
Methyl mercury has a relatively long half-life in human tissue
and can accumulate in individuals who consume contaminated
fish and fish oils on a regular basis. Skinning and trimming is
usually recommended to reduce exposure to contaminants but
because methyl mercury is distributed throughout the muscle,
skinning and trimming does not significantly reduce mercury
concentrations in fillets. Pregnant and lactating women as well
as children are generally advised against the consumption of
shark, swordfish, king mackerel and tilefish, since these species
may contain higher levels of mercury.
32
Our analysis has shown
that mercury was virtually absent in the oils present in the South
African samples and it is therefore not of any health concern.
It is undoubtedly the responsibility of manufacturers to
provide accurate information on supplement labels to protect
the consumer against misleading health and nutrient claims,
to ensure the safety of the consumer and to guarantee a high-
quality, consistent product. However, in South Africa this does
not seem to be the case.
Possible reasons for substandard supplements on the South
African market may include: poor quality of imported fish oil,
seasonal differences in EPA and/or DHA concentrations of
imported fish oils, lack of proper labelling legislation of food
supplements, inappropriate handling of fish oil when harvested,
improper storage conditions of both fish oil and supplements,
oxidation of fatty acids, ineffective quality assurance by supple-
ment manufacturers, and infrequent or poor batch-control analy-
ses. If these issues are not addressed and legislation on food
supplements is not enforced, South African consumers will have
to deal with substandard dietary supplements.
Conclusion
More than half of the n-3 supplements available on the South
African market contained less than the amount of EPA and/or
DHA content as claimed on the labels of the products, which has
considerable cost implications for the consumer. Early indicators
of rancidity in the majority of capsules suggest a wide variation
in the quality of the marine oils present in the n-3 capsules avail-
able on the South African market. This is despite the addition of
vitamin E as antioxidant. South African n-3 fatty acid supple-
ments appear to be virtually free of methyl mercury.
We thank Mr Francois Wewers from the Department of Chemistry, CPUT for
the determination of the mercury content of the fish oil capsules.
References
1.
Kris-Etherton PM, Innis S. American Dietetic Assocition and Dietitians
of Canada. Position of the American Dietetic Association and Dietitians
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J Am Diet Assoc
2007;
107
(9): 1599–
1611.
2.
Woodside JV, Kromhout D. Fatty acids and CHD.
Proc Nutr Soc
2005;
