Pregnant women are advised to pay particular attention to food hygiene during pregnancy and also to avoid certain foods, in order to reduce the risk of exposure to substances that may be harmful to the developing fetus. Potentially harmful substances include food pathogens (e.g. listeria and salmonella) and toxic food components [e.g. dioxins and polychlorinated biphenyls (PCBs)], as well as alcohol and high doses of some dietary supplements (e.g. vitamin A).
Vitamin A Dietary vitamin A is obtained in two forms: as the preformed vitamin (retinol) which is found in some animal products such as dairy products, liver and fish liver oils, and as vitamin A precursors in the form of carotenes which are found in many fruits and vegetables. It is well known that excessive intakes of vitamin A in the form of retinol may be toxic to the developing fetus.
Vitamin A has been shown to be teratogenic (cause malformations in an embryo or fetus) in animals, and a number of epidemiological studies in humans have indicated that exposure to high levels of vitamin A during pregnancy may increase the risk of birth defects. The dose threshold for prevention of birth defects is still unclear, but the lowest supplemental dose associated with teratogenic effects is 3000 μg per day (Rothman et al. 1995). This has been
suggested as the dose threshold for teratogenicity (EVM 2003).
Women who are pregnant or may become pregnant should avoid taking supplements containing retinol (including high dose multivitamins) and cod liver oil supplements, unless advised to do so by their physician.
A healthy and varied diet should provide sufficient vitamin A. Other sources of vitamin A in the diet (e.g. dairy products, fat spreads, eggs, carrots and leafy vegetables) do not pose any risk of excessive intakes, and should be included as part of a healthy, balanced diet during pregnancy.
Alcohol consumption in high amounts has been shown to affect reproduction in women, influencing the ability to conceive and the viability of conception (Goldberg 2002). Furthermore, heavy alcohol intake in early pregnancy can have potentially damaging consequences on the embryo. Women who might become pregnant are therefore advised to avoid excessive intakes of alcohol, as any adverse effects on the fetus could occur before pregnancy has been confirmed.
Drinking heavily throughout pregnancy, i.e. intakes of more than 80 g of alcohol per day (equivalent to 10 units) is linked with an increased risk of fetal alcohol syndrome (FAS). This is characterised by reduced birthweight and length, including a small head size and a variety of congenital abnormalities, as well as a characteristic facial appearance. Affected children can exhibit mental retardation and stunted physical growth, although not all infants exhibit all the features of FAS (Beattie 1992).
The effects of FAS may be more severe where maternal nutritional deficiencies also exist, which frequently occurs with alcohol abuse. Intake of B vitamins is often low, while requirements may be increased due to excessive alcohol consumption. Serum concentrations of antioxidant vitamins are reduced by excessive alcohol intakes, yet these nutrients are essential in protecting against alcohol-induced free radical damage in maternal and fetal tissues. Alcohol also has a detrimental effect on the absorption and utilisation of folate, thus compounding the problem of inadequate peri-conceptual folate intakes in women who drink alcohol heavily.
Caffeine The Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT 2001) has recently reviewed the evidence on the reproductive effects of caffeine.
A number of studies have shown an association between maternal caffeine intakes during pregnancy and an increased risk of both LBW and spontaneous abortion. However, the research has not found a threshold of caffeine intakes, above which there is a definite risk to pregnancy.
The Committee considered that there is plausible evidence of an association between caffeine intakes above 300 mg per day (around four cups of coffee).and LBW as well as spontaneous abortion. Caffeine is present in a variety of foods and beverages, including cocoa, colas, energy drinks and chocolate, as well as tea and coffee. Note that the caffeine content of beverages, such as tea and coffee, varies greatly depending on brewing method, brand and strength. Caffeine is also found in a number of prescription and over-the-counter medicines, e.g. headache pills, cold and flu remedies, diuretics and stimulants (COT 2001). Typical caffeine contents of several foods and drinks are shown in Table. In reality, as with alcohol, many women spontaneously reduce their consumption of caffeinated drinks, such as coffee, during pregnancy.
Caffeine contents of commonly consumed beverages and food
|Beverage or food||Serving size||Caffeine content|
|Instant coffee||190 ml cup||Approx. 75 mg|
|Brewed coffee (filter or percolated)||190 ml cup||Approx. 100–115 mg|
|Decaffeinated coffee (instant or brewed)||190 ml cup||Approx. 4 mg|
|Tea||190 ml cup||Approx. 50 mg|
|Drinking chocolate||200ml||1.1–8.2 mg|
either added caffeine
|250ml||28 – 87mg|
|Cola (regular and diet)||330 ml||11–70 mg|
|Chocolate||50 g bar||5.5–35.5 mg|
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