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Know your dietary supplements

Is that supplement you’re taking vital to optimum health? Research scientist Bridget Carmady reports on the implications of four of our most popular pills.

Omega-3 fatty acids found in oily fish are an important part of keeping your brain and body healthy. These fatty acids are associated with improved brain, heart, joint, bowel and eye health.

Most fish oil capsules contain 1000mg (milligrams) fish oil, of which 300mg are omega-3 fatty acids. While there is no recommended dietary intake (RDI) for omega-3, the Ministry of Health suggests an adequate intake is 160mg for men and 90mg for women. The suggested dietary target to reduce chronic disease, however, is 610mg for men and 430mg for women. This equates to taking two fish oil capsules a day for general health, although you are likely to already get some from food.

When to take fish oil

You can get a lot more bio-available fish oil from oily fish than from fish oil capsules. And if you are consuming such fish, you don’t need to take fish oil capsules.
Studies, however, suggest that fish oil supplements are a sensible addition to your diet if you have cardiovascular disease, arthritis, asthma or a mental health disorder such as depression or ADHD. They are probably also not a bad idea for general health, especially if you can’t be convinced to eat fish!

When NOT to take fish oil

Studies show that you will gain greater benefit by eating two serves of fish each week (such as a small piece of salmon and a can of tuna) because we absorb a lot more omega-3 directly from fish, rather than fish oil supplements. In fact, just 100g of farmed King salmon contains over 3000mg omega-3s – more than 10 times the amount found in a fish oil capsule!

Fish oil supplements are generally considered safe for people with fish or seafood allergies as the proteins which cause the allergic reaction are removed in the manufacturing process, but be sure to consult with your doctor before taking any supplements. As yet, no studies have reliably shown that people with a fish or seafood allergy will not have a reaction to fish oil capsules.

Hot tip

There are other types of omega-3 supplements such as krill oil (which is being touted as a more sustainable alternative) or micro-algae (a vegan option) – which may be a better choice for you if you have allergies.

Most calcium supplements are not sold in doses higher than 500mg, as the body doesn’t absorb calcium in amounts larger than this. For both men and women, the RDI for calcium is 1000mg – equivalent to two cups of milk (either cows’ milk or calcium-fortified soy) plus one 200g tub of yoghurt.

When to take calcium

Daily calcium requirements jump to 1300mg for women during certain life stages, such as pregnancy, breastfeeding and after menopause, as well as for men over 70 years of age, and for all teenagers – the equivalent of four to five serves of dairy each day.

When NOT to take calcium

Calcium supplementation has been shown to help reduce the risk of osteoporosis, bone fractures, kidney stones and, if it’s in your family’s history, colorectal cancer. If you are at risk of any of these, supplements may be a good idea, but talk to your GP first. You may need to be aware of interactions with medications, and women over 70 with coronary heart disease are advised not to take calcium supplements.

If you’re already getting three to four dairy serves each day, calcium supplements aren’t a good idea.

Hot tip

Most calcium supplements contain calcium carbonate and need to be taken with food to be broken down by stomach acids. For a supplement that can be taken without food, choose one made with calcium citrate.

Probiotics are bacteria that help balance the bacterial population of the gut. Probiotics need to be alive to be effective so always check the use by date. Most products have a shelf-life of three to six weeks and up to 12 months for capsules.

When to take probiotics

Antibiotics and other drugs, stress, too much alcohol and an unhealthy diet can all upset the balance of bacteria in the gut, so taking probiotics could help. The strongest evidence for their beneficial effect is around diarrhoea from antibiotics or infection and there is evidence they can help with inflammatory bowel disease and ulcerative colitis. The evidence is less conclusive for irritable bowel syndrome, certain allergic disorders and urinary tract infections.

When NOT to take probiotics

If you don’t have a specific need for probiotics, they may still help to strengthen the immune system although more research is needed. The only harm they could do might be to your wallet.

Hot tip

Not all probiotics are equal. Health benefits appear to be strain-specific so look for products that are clinically proven and tell you what they’re good for.

Zinc is beneficial in a number of ways including helping clear up eczema, helping wounds heal faster and maintaining a healthy immune system. It is also essential to a healthy reproductive system.

We only require a small amount of zinc – with an RDI of 8mg to 14mg for healthy men and women. Supplements, therefore, only contain small amounts of the mineral (5mg to 25mg). For comparison, one large oyster or 160g steak provides 8mg zinc.

Zinc absorption is lower from vegetarian diets, so intakes need to be up to 50 per cent higher for people not eating meat. Having one cup of chickpeas or baked beans and a small handful (30g) of almonds or cashews each day will help vegetarians and vegans meet zinc requirements.

When to take zinc

Zinc is most readily available in meat, eggs and seafood, so those who don’t eat these foods, such as vegans, could consider zinc supplementation. People with conditions that can cause poor nutrient absorption (such as IBS and coeliac disease) may also need to supplement their diet with zinc. Research has shown that zinc can reduce the severity and duration of a cold, so it may be worth taking if you take it within a day of feeling a cold coming on.

When NOT to take zinc

Like calcium, if you are already meeting your zinc RDI through your diet, taking a supplement is not recommended. Zinc from supplements can be toxic in large doses and the Ministry of Health recommends no more than 40mg per day for men and women from all sources.

Hot tip

Zinc is extremely important for fertility, especially sperm health, so be sure to get your RDI of zinc if you are planning to start a family.

Supplements can be money well spent, whether you need them to help with an existing health issue (eg. fish oil for arthritis), or to prevent health problems from cropping up when you are not able to get enough of a particular mineral from your diet (eg. calcium to ward off osteoporosis). They are not a cure-all, though.

Ultimately, a balanced diet should normally provide you with sufficient nutrients to keep you in good health.

Recommended supplements

Vitamin B12Vitamin B12 is found naturally only in animal foods so fortified foods or supplements must be used by vegetarians and vegans to ensure an adequate intake of B12. This is especially important for women of childbearing age and for older people.

Folic acidThe Ministry of Health recommends women take folic acid tablets for at least four weeks before and for 12 weeks following conception to reduce the risk of neural tube defects (NTDs). The only subsidised registered medicines available over the counter from pharmacies, which they recommend, are an 800mcg (microgram) tablet for women at low risk of NTDs and a 5mg (milligram) folic acid tablet for women at high risk.

IodineDue to their increased need for iodine the Ministry of Health recommends pregnant and breastfeeding women take a registered 150mcg iodine-only tablet each day. Iodine is essential for brain development and growth of the foetus and infant. Despite mandatory fortification of bread with iodine since 2009, it is difficult for pregnant and breastfeeding women to meet their increased iodine needs.

Date modified: 5 December 2017
First published: May 2011


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