Even the most popular vitamin supplements have little scientific backing.
Two-thirds of us take vitamin and mineral supplements in the hope they’ll protect our health (especially if we’re not eating properly) or give us a boost when we’re run down. However, despite their popularity, most supplements are no better than a placebo. Unless the product is doctor-recommended, you’re better off splashing the cash on foods that’ll help you achieve a balanced diet.
Last year, Kiwis forked out $116 million on vitamins, minerals and herbal extracts at the supermarket, according to market research company Nielsen. We’ve investigated the claims for some of the most popular supplements on shop shelves.
Supplement claims: “Magnesium is an important nutrient for the cardiovascular system” “... helps relax tight muscles” “... support restful sleep”
Is the supplement effective? Although there’s some promising research into magnesium and blood pressure, the jury remains out. As for the other claims? They aren’t backed by good science.
Summary of the science: Magnesium’s role in promoting cardiovascular health may look promising but it’s still early. Although the Cochrane Collaboration (an independent group of researchers that systematically reviews scientific evidence) concluded there was no evidence magnesium had an effect on blood pressure back in 2006, two more recent reviews found a positive effect. However, both found further (and better-quality) research was needed before we could be sure.
In 2012, claims magnesium supplements eased muscle cramps were put to the test by Cochrane researchers. This review – and similar scientific reviews in 2014 and 2015 – found the evidence unconvincing. A clinical trial run since found no difference between magnesium and placebo pills on cramp pain or duration.
Tip: dehydration can worsen muscle cramps – so reach for a glass of water, rather than a magnesium tablet.
There’s also very limited research on magnesium and insomnia – one clinical trial found a supplement helped elderly people with low intakes of the mineral to drop off to sleep 10 minutes faster, though there was no significant difference in the total hours they slept. Until this result is replicated across multiple studies using thousands of people with normal magnesium intake, be sceptical of these claims.
You’re best off getting the mineral in food. If your magnesium stores are low, your body will adjust so it absorbs more of the nutrient.
Dietary sources: Legumes (eg black beans); nuts (eg almonds, cashews); seeds (eg pumpkin seeds); whole grains; leafy green vegetables (eg spinach); fortified breakfast cereals; milk.
Supplement side effects: High intakes of magnesium are linked to abdominal cramping, diarrhoea and nausea. Very high doses can cause an irregular heartbeat or a heart attack. Magnesium supplements can interfere with medications from antibiotics to osteoporosis drugs.
Also known as: Alpha-linolenic acid or ALA, eicosapentaenoic acid or EPA, docosahexaenoic acid or DHA
Supplement claims: “... support a healthy heart and cardiovascular system” “…support the development of a healthy baby” “…helps support brain and cognitive health” “…maintain normal vision and eye health”
Is the supplement effective? Only if you’re pregnant and don’t eat fish regularly – if so, have a chat with your doc. Otherwise, there’s little robust evidence supporting the benefits of omega-3 supplements available over the counter.
Summary of the science: When the Cochrane Collaboration evaluated the importance of omega-3s in pregnancy in 2018, it found an increased intake of these fatty acids – either through diet or supplements – reduced the risk of pre-term births and lower weight babies.
The Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) suggests pregnant women who eat little seafood may want to consider a dietary supplement of fish oil.
Outside of pregnancy, things aren’t as clear-cut. There’s a link between eating plenty of fish and heart health – but when scientists give people fish oil pills, there isn’t always a corresponding drop in disease. Two 2018 studies (one by Cochrane researchers) found no good evidence omega-3 supplements had any effect on cardiovascular health.
Shortly after, a new clinical trial concluded a highly purified form of omega-3 did reduce cardiac events from strokes and heart attacks, though the tablet is a prescription medicine only approved in a few countries (such as the US) and very different to what you’d find on shelves here.
The evidence for the other touted benefits of omega-3 supplements – from cognitive to eye health – is inconsistent.
All in all, healthy adults are better off getting omega-3s from food.
Dietary sources: Fish and seafood (eg salmon, mackerel, tuna provide EPA and DHA); seeds (eg flaxseed, chia seeds provide ALA); nuts (eg walnuts provide ALA); plant oils (eg flaxseed, soybeans, canola oils provide ALA).
Supplement side effects: From bad breath to headaches and nausea, these are usually mild. However, very high doses of fish oil can cause bleeding problems or affect your immune system. The pills can interfere with blood-thinning medication.
Also known as: Ascorbic acid
Supplement claims: “Well known as the immunity vitamin” “… helps relieve cold symptoms” “… supports wound healing and healthy skin” “… assists in iron absorption”
Is the supplement effective? There isn’t enough evidence to justify supplements, especially as most Kiwis already get plenty of vitamin C. When it comes to the common cold though, watch this space.
Summary of the science: The research indicates adults who take vitamin C regularly experience slightly shorter colds than those who don’t – though there’s no effect on the number of bugs they catch. Even so, Cochrane researchers remained sceptical, concluding in 2013 there wasn’t enough evidence to recommend the supplement. Its researchers are in the middle of reviewing the research again, so we’ll keep you posted.
While prolonged vitamin C deficiency can cause skin problems (among other things), a nutritional survey in 2006 found only two percent of Kiwis had an inadequate intake. Additionally, if our intake is low, our bodies will adjust to absorb more.
There’s little evidence healthy adults’ skin will be improved if they take vitamin C pills.
Vitamin C is thought to boost the amount of iron your body absorbs from plant materials. However, researchers are unsure if large amounts of the vitamin work any better than small amounts or if it helps you absorb iron from other sources (such as an iron tablet). If you’re iron deficient, eat vitamin-C rich foods alongside your sources of iron – there’s nothing to suggest supplements do a better job.
Two robust clinical trials have concluded a combination pill including vitamin C, E, copper, zinc and carotenoids can slow the progress of age-related macular degeneration, a vision-degrading disease. However, there’s no evidence it prevents the condition.
Dietary sources: Citrus fruits; capsicum; kiwifruit; broccoli; strawberries; tomatoes; fortified foods and drinks (eg fruit juice).
Supplement side effects: If you take large amounts of vitamin C, you might experience diarrhoea, nausea and stomach cramps. The supplements can interfere with medicine, including chemotherapy drugs and statins.
Often combined with: Garlic and echinacea
Supplement claims: “… helps build up an all-year-round resistance against colds and flu”
Is the supplement effective? Not particularly.
Summary of the science: In a 2014 review of clinical trials, Cochrane researchers found echinacea offered no more than “small preventive effects” based on weak evidence. It found the science supporting garlic even less convincing.
Also known as: Curcumin
Supplement claims: “… used in Western herbal medicine to temporarily relieve mild joint pain and inflammation” “… may have mild anti-inflammatory properties”
Is the supplement effective? There aren’t enough well-designed studies to tell.
Summary of the science: Only a handful of preliminary studies have tested the effects of turmeric on joint pain. So although there appears to be a positive effect, the researchers of a 2016 review concluded more (and better-quality) research was needed before any judgement could be made.
The same is true for claims on turmeric’s anti-inflammatory effects. Companies shouldn’t be making these types of claims, based on such flimsy evidence.
Sourced from: Curcuma aromatica and Curcuma longa plants.
Supplement side effects: The plant extract may cause digestive issues if taken in high doses or for a long time.
Supplement claims: “Ease joint pain and rebuild cartilage” “… help reduce joint swelling and inflammation” “… aid in the maintenance of normal joint function”
Is the supplement effective? Definitive evidence for the claimed benefits has yet to be found.
Summary of the science: A 2017 clinical trial threw up a concerning finding: the placebo actually outperformed the glucosamine-chondroitin pill, suggesting the supplement may make joint pain worse. This result directly conflicted the findings from several research reviews (including one done by Cochrane researchers in 2015) that found chondroitin and glucosamine helped to reduce pain (albeit at a small to moderate level).
It’s a similar story for joint function: there’s nothing definitive. The only way to de-muddy the waters is by putting the compounds to the test in robust clinical trials in future.
Sourced from: Shellfish or corn (glucosamine); synthetic production or shark or cow cartilage (chondroitin)
Supplement side effects: The compounds may cause abdominal pain and diarrhoea as well as interfere with the way your body handles sugar. The combination supplement may interfere with blooding-thinning medication. However, serious side effects are rare.
Supplement claims: “Fights fatigue, boosts energy” “Energy and immunity”
Is the supplement effective? Only if you’ve been diagnosed as iron deficient.
Summary of the science: According to the most recent nutrition survey back in 2006, one in 10 Kiwi women and one in 100 men get inadequate iron in their diet, which can reduce the number of red blood cells they have (known as anaemia). Anaemia has various causes, but often leaves you tired and weak. You may take longer to fight off an infection. For those with iron-deficiency anaemia, supplements should treat those symptoms.
However, check with your GP before stopping by the supplement aisle. Another cause of dizziness and fatigue is iron over-absorption (known as hemochromatosis). The disease causes liver and heart damage, so loading up on iron can be life-threatening.
Most research focuses on iron’s ability to treat anaemia – very little has measured its effects on healthy people’s energy levels or ability to fight infections. As such, products need to make it clear claims only apply to people with deficiencies.
Unless a doctor tells you otherwise, you’re best off getting your daily iron from food. This is true for pregnant women as well, according to RANZCOG – though you’ll be offered a blood test to check your levels.
To a point, your body naturally compensates if you have low iron stores by absorbing more from what you eat. That said, vegetarians and vegans should keep an eye on their intake. Tea-drinkers: the tannins in your cuppa may interfere with absorption, so you may want to avoid pairing the beverage with meals.
Dietary sources: Lean meat (eg red meat, poultry); seafood; iron-fortified food (eg cereal); bread; lentils and kidney beans; spinach; green peas
Supplement side effects: In high doses, iron supplements can cause abdominal pain, constipation, fainting, nausea and vomiting. It can also mess with the amount of zinc you’ll absorb.
Often combined with: Vitamin C.
Supplement claims: “Digestion and circulation support” “Helps reduce travel or motion sickness”
Is the supplement effective? There isn’t enough robust evidence to be certain.
Summary of the science: In 2015, Cochrane researchers assessed seven clinical trials testing how effectively ginger could combat morning sickness compared with a placebo. Some of the studies found ginger outperformed the placebo but researchers concluded the “evidence overall was not consistent”. There’s been little large-scale research since, so the picture remains unclear.
The ability of ginger to lower blood pressure has only been put to the test in a small number of preliminary studies with low numbers of participants. Although early results appear favourable, further studies with higher numbers of patients are needed. Until then, healthy scepticism is warranted.
Sourced from: Zingiber officinale plant.
Supplement side effects: Ginger’s side effects are typically mild. They include abdominal discomfort, diarrhoea, gas and heartburn. The extract may interfere with blood-thinning medication.
Supplement claims: “Helps maintain and develop healthy bones” “… may help prevent osteoporosis” “Helps support healthy bones and teeth”
Is the supplement effective? Other than for pregnant women, it’s doesn’t look like it. Concerningly, the tablets may have nasty side effects.
Summary of the science: As calcium is a key component of our skeleton, it’s been suggested a higher intake of the mineral would boost bone health, particularly in those suffering from osteoporosis (where bones become weak and prone to fractures).
This theory has been tested in clinical trials of calcium supplements but results have been mixed. Some trials – particularly those using patients in aged-care homes or with low calcium intakes – demonstrated a benefit. Others found zero effect compared with a placebo.
In 2019, University of Auckland researchers, including Professor Ian Reid, reviewed the evidence and concluded “extra calcium doesn’t make any difference” to adults in good health.
The controversy is only likely to be resolved with further, good-quality research.
According to Cochrane researchers, there’s some evidence that calcium supplements may reduce pregnancy health issues, including pre-eclampsia. The mineral is also vital to building a baby’s skeleton. On this basis, RANZCOG recommends pregnant women who eat little dairy consider calcium supplements.
Outside of pregnancy, speak to your doctor about your calcium intake if you avoid dairy products. Otherwise, Professor Reid said getting calcium through a balanced diet (which includes minimal alcohol and no tobacco), maintaining a healthy weight and staying active will boost your bone health better than a calcium tablet.
Dietary sources: Dairy products; fortified foods (eg soy and rice milks, tofu); kale; broccoli; Chinese cabbage; grains (eg bread, pasta); sardines.
Supplement side effects: Calcium supplements, particularly high-dose tablets, can cause constipation and kidney stones and may be linked to cardiovascular disease. The pills may also interfere with the body’s absorption of other key nutrients, such as iron and zinc.
Often combined with: Vitamin D
Supplement claims: “For strong bones and immunity” “Helps support bone health and calcium absorption”
Is the supplement effective? The evidence supporting bone health claims is murky at the moment. But if your skin doesn’t see a lot of sunshine or you have dark skin, ask your doctor about supplements.
Summary of the science: Cochrane researchers last compiled the evidence for the effect of the “sunshine vitamin” on bone health in 2014. Alone, vitamin D didn’t appear to have any effect, though the researchers noted some studies using calcium-vitamin D pills had produced positive results.
Since then, Professor Reid’s 2019 study (and several others) concluded there was no evidence to support vitamin D supplements if you’re a healthy adult living at home. New clinical trials are needed to resolve the debate.
It’s been speculated vitamin D can boost immunity, since the nutrient helps to activate some of the body’s immune responses and is often lower in people who’ve recently had an infection. A handful of trials tested the theory but a 2016 Cochrane review (based on young patients) found no evidence to support it.
One explanation is that ill people spend more time inside and less in the sun. For many of us, our bodies get most vitamin D by making it, using the sun’s rays to convert cholesterol into the micronutrient.
Without adequate sun exposure, you can become deficient – so if you wear veils, have very dark skin or don’t get outdoors often, it could pay to speak to your doctor about a vitamin D supplement. Although the body can store the vitamin, the Ministry of Health suggests residents in the lower South Island chat with their GP about using supplements during the winter months.
Although the research into vitamin D in pregnancy is inconsistent, RANZCOG recommends supplements. If you’re pregnant (or are planning to be), have a chat with your doc or midwife.
Otherwise, you’re best off getting vitamin D through our diet and skin (though remember to slip-slop-slap in summer).
Dietary sources: Fish (eg salmon, tuna, mackerel); beef liver; cheese; eggs; mushrooms.
Supplement side effects: Taking too much vitamin D may cause appetite and weight loss, constipation, nausea, vomiting and weakness. It can also damage your kidneys. Very high doses increase the risk of falls and fractures. It also messes with your calcium absorption, causing confusion and heart problems.
Supplement claims: “Helps maintain healthy skin” “… helps maintain resistance to infection” “… support healthy immunity”
Is the supplement effective? Zinc tablets may shorten colds but at the high level required you may be swapping a runny nose for nausea. Other claims are sketchy.
Summary of the science: Since zinc plays a key role in the immune system, researchers have wondered if supplements could prevent infections.
There’s growing evidence high-dose zinc pills, taken when common cold symptoms are first noticed, may help adults fight off bugs more quickly. Some researchers are convinced of its effectiveness, while others warn more research is needed. A major issue is that serious side effects often result from the doses required to have an effect, which could outweigh any benefits.
Though children on zinc pills developed pneumonia less frequently, the trials were conducted in lower-income countries where zinc deficiency is more likely. This doesn’t mean the same effect would be seen in people eating a balanced diet. The studies on ear infections had inconsistent results.
As a proportion of our body’s zinc resides in our skin, a deficiency of the mineral can cause rashes and slow wound healing. However, there’s little to suggest healthy adults who get recommended amounts of zinc will see any improvement from supplements.
In the most recent nutritional survey, two in five Kiwi men (particularly the over-50s) and one in 10 Kiwi women received insufficient levels of the mineral from their diet. Vegetarians and vegans in particular need to ensure their diet includes zinc-rich foods. Unless your doctor recommends supplements, it’s best to get your daily requirements from what you eat and drink.
Dietary sources: Oysters; lean meat (eg red meat, poultry); seafood (eg crab, lobster); fortified foods (eg cereal); beans; nuts (eg cashews); whole grains (eg buckwheat); dairy products.
Supplement side effects: High doses can cause appetite loss, diarrhoea, headache, nausea, stomach cramps and vomiting. Over the long term, too much zinc can interfere with your copper absorption and “good” cholesterol.
Supplement claims: “… enhances the healing of burns, scars and wounds” “… helps prevent premature aging” “… assists in protecting against cardiovascular disease and diabetes”
Is the supplement effective? We’re still unsure whether the benefits of vitamin E pills outweigh some worrying potential harms.
Summary of the science: The vitamin’s ability to heal rashes, scars and wounds produced conflicting results in a few small-scale trials – making these claims dubious.
Its impact on cardiovascular health has been better studied. However, experts disagree about what the combined findings tell us. Although some reviews of the evidence have found a slight improvement in cardiovascular health, other expert groups were concerned the supplement may do more harm than good.
This included Cochrane researchers, who concluded in 2012 “vitamin E seems to increase mortality”. One large clinical trial, which wrapped up in 2011, found men taking a vitamin E supplement had a higher chance of developing prostate cancer than those taking a placebo.
With findings like these in mind, the US Preventive Services Task Force (a volunteer panel of medical experts) recommended people not take vitamin E supplements for the prevention of cardiovascular disease and cancer. It’s currently reviewing the latest evidence. We’ll keep you posted if anything changes.
With the science up in the air, ditch the pills in favour of a balanced diet unless your doctor says otherwise. New Zealanders typically get plenty of vitamin E already.
Dietary sources: Plant oils (eg wheatgerm, sunflower, safflower); nuts (eg almonds, peanuts, hazelnuts); seeds (eg sunflower seeds); spinach; broccoli; fortified foods (eg cereal).
Supplement side effects: High doses of vitamin E may reduce your body’s ability to form blood clots, increasing your risk of bleeding – including serious bleeding in the brain. The supplements may interfere with blood-thinning, cholesterol and cancer medication.
Paradoxically, studies show those who take supplements may already have more nutritious diets than those who don’t.
A 2011 research paper compared the diets of Americans who used supplements against those who didn’t, and found the former group received more magnesium, copper and potassium from their food and drink than the others. Concerningly, some supplement users were getting excessive levels of calcium, zinc, iron and magnesium.
A similar study back in 2005 found New Zealanders were taking supplements unnecessarily, as the participants’ nutrient intake from food and drink alone was perfectly adequate.
If you’re looking for something to boost your health and reduce your disease risk, walk past the supplement store – and keep going. Regular physical activity reduces your risk of dying early, no matter the cause.
To meet your nutritional needs, each day eat:
Dietary supplements are laxly governed by 35-year-old regulations, which don’t require manufacturers to get approval before putting their products on the market.
A product that didn’t provide the nutrients or dose listed on the label would breach the supplement regulations and the Fair Trading Act, which could see the company hit with a maximum $600,000 fine. However, the only way to tell if a pill contains 1000mg or 1mg of a nutrient is via expensive testing.
There’s also no pre-vetting of claims. Although dietary supplements can’t claim to treat or prevent a condition, suppliers get around this by using vague language, such as “may assist”, “can support” or “may help”.
In the EU, supplement manufacturers must submit evidence to the European Food Safety Authority and have a claim approved before they can put it on their packaging or advertising materials. The authority has only approved a small fraction of all submitted claims and said there wasn’t enough evidence backing extracts such as glucosamine and turmeric. We’d like to see a similar pre-vetting system introduced in New Zealand.
Several products we found on supermarket shelves are out of step with the nutrient recommendations set by the Australian and New Zealand health ministries. Government guidelines recommend you have no more than 350mg of magnesium (in the form of supplements) each day – above this, you’re likely to get tummy upsets. We found one product, Healtheries Magnesium 400mg High Strength, exceeding it.
A Healtheries spokesperson said it’s not required by law to consult these government guidelines when formulating a product. The regulations don’t limit the amount of magnesium allowed in supplements (though do impose limits for minerals such as iron and zinc).
We think responsible companies should regularly review the science to ensure their products don’t put customers at risk of unpleasant side effects.
The ministries’ recommendations also note 1000mg of vitamin C in tablet form each day is a “prudent limit”. Still, we found several products – including Cenovis Mega C 1000mg – advising consumers to take up to 3000mg daily, putting users at risk of tummy troubles or acid build-up.
A spokesperson for Sanofi (which owns the Cenovis brand) said the product’s dosage was reviewed and adjusted down in 2019. Products with the new labels, advising consumers to take one to two 1000mg tablets per day, “are now beginning to be shipped,” the spokesperson said.
The Australasian obstetrician and gynaecology association, RANZCOG, recommends healthy pregnant women, in addition to eating a balanced diet, take daily supplements containing:
It’s best to discuss these recommendations, alongside your diet and nutrient intakes, with your doctor.