Daily Multivitamins: Benefits, Risks & Research

Updated 12 October 2026. Daily multivitamins can help address nutritional shortfalls, and recent American clinical trials suggest they may modestly improve certain measures of memory in older adults. However, routine use has not been shown to prevent heart disease or extend life in healthy people. This article compares major US studies with Australian nutrition and supplement guidance.

Key takeaways

Multivitamins can help address nutritional shortfalls, but large clinical trials have not shown that routine use prevents cardiovascular disease or extends life. The cognitive results from COSMOS are modest and promising, not proof of dementia prevention. Cancer trial results are mixed.

Outcome	What the evidence suggests
Nutrient intake	Can increase intake of nutrients actually included in the product
Memory and thinking	Small improvements on cognitive testing among older adults in COSMOS
Dementia	No proven preventive benefit
Cancer	Mixed findings across PHS II and COSMOS
Heart disease	No convincing preventive benefit
Longevity	No demonstrated mortality benefit

1. What is a multivitamin?

A multivitamin/mineral supplement combines several vitamins and minerals, sometimes with other ingredients. Products differ considerably in content and dose. They may contain vitamins A, C, D, E and B vitamins as well as zinc, iron, selenium, calcium and magnesium. Some omit important minerals or provide only small amounts. A supplement designed for older adults may differ from one intended for pregnancy or children. Improving nutrient intake does not automatically prevent disease. NIH multivitamin fact sheet.

2. How many Australians take multivitamins?

The Australian Bureau of Statistics reported that 15.5% of Australians aged two and older used multivitamin or multimineral supplements in 2023, including 21.3% of people aged 65–74. Across all types, 33.6% used a dietary supplement. These data describe reported use, not proof of improved health.

Australian population	Multivitamin/multimineral use
All people aged 2+	15.5%
Ages 65–74	21.3%

ABS Dietary Supplements, 2023.

3. Filling nutrient gaps: where multivitamins can help

The clearest benefit is increasing intake where a diet is low in particular nutrients. Historical US survey estimates found intake below estimated average requirements for vitamin D (about 70%), vitamin E (60%), magnesium (45%), calcium (38%), vitamin A (34%) and vitamin C (25%). These are estimates of inadequate dietary intake, not diagnosed deficiencies or current Australian prevalence figures. Nutritional benefits depend on the formulation and baseline diet; multivitamins often contain relatively little calcium or magnesium. Australian vitamin D research also shows that deficiency occurs despite abundant sunlight. People with an established deficiency may require targeted treatment rather than a general multivitamin. See the NIH evidence summary and ABS data.

4. COSMOS-Web: can multivitamins improve memory?

In the American COSMOS-Web randomised clinical trial, 3,562 older adults were assigned a daily multivitamin or placebo and completed internet-based cognitive tests. Those receiving multivitamins performed better on the primary episodic-memory outcome after one year. Researchers interpreted the test difference as corresponding to about three years of age-related change on that measure, but it does not mean participants became biologically younger or avoided dementia. The research tested a particular formulation in older adults, not all products in all ages. Yeung et al., 2023.

5. COSMOS cognitive studies: combined evidence

A 2024 pooled analysis of three COSMOS cognitive substudies found a small advantage of approximately 0.07 standardised units in global cognition and 0.06 in episodic memory. Investigators compared the global cognition difference to about two years of cognitive ageing. These estimates are statistical interpretations of modest test-score differences. The substudies arose within the same programme rather than three completely independent trials. The earlier Physicians’ Health Study II cognitive substudy did not find a significant overall benefit. Independent replication remains important. Vyas et al., 2024.

6. Do multivitamins prevent dementia?

COSMOS-Mind followed 2,262 participants for roughly three years and reported 110 incident cases of mild cognitive impairment and 14 cases of probable dementia. Supplementation did not significantly reduce either outcome. The small dementia case count limits precision. Improving some cognitive test scores is not equivalent to demonstrating that a supplement prevents Alzheimer’s disease or dementia. Sachs et al., 2023.

7. Cancer: Physicians’ Health Study II

PHS II enrolled 14,641 US male physicians aged 50 or older and followed participants for a median of around 11.2 years. A daily multivitamin was associated with an 8% relative reduction in total cancer (hazard ratio 0.92); no significant reduction was established for individual cancers including prostate cancer. Absolute differences were modest and a trial limited to male physicians cannot directly establish benefits for women or the wider population. Gaziano et al., 2012.

8. COSMOS: a different cancer result

COSMOS randomised 21,442 older American adults and followed them for a median of about 3.6 years. There were 518 invasive cancers among participants taking multivitamins versus 535 with placebo: no statistically significant reduction. COSMOS also found no significant overall cardiovascular benefit. Shorter follow-up, different populations and other factors could explain differences from PHS II, but none is proven. Multivitamins are not established cancer-prevention treatment. Sesso et al., COSMOS 2022.

9. Heart disease and stroke

PHS II observed 867 major cardiovascular events in the multivitamin group and 856 in the placebo group, with no statistically significant overall protection against major cardiovascular events. COSMOS likewise found no significant multivitamin benefit for its cardiovascular outcomes. A possible benefit of cocoa extract studied in COSMOS should not be attributed to multivitamins. Proven prevention involves appropriate blood-pressure and cholesterol management, exercise, diet, avoiding tobacco and recommended medical care.

10. Do multivitamins help people live longer?

A 2024 US National Cancer Institute analysis included 390,124 adults in three prospective cohorts followed for up to 27 years. It found no association between daily multivitamin use and lower mortality. In the first part of follow-up, adjusted mortality hazard ratio was about 1.04 for daily users, but observational research cannot establish that multivitamins caused harm; confounding remains possible. The appropriate conclusion is that no longevity benefit was demonstrated. PHS II also found no significant overall mortality benefit. Loftfield et al., 2024.

11. Cataracts and eye health

A PHS II analysis recorded 872 cataracts in multivitamin users compared with 945 in placebo, a 9% relative reduction in older male physicians; the estimated reduction for nuclear cataracts was about 13%. The study did not demonstrate significant benefit for age-related macular degeneration. Findings require caution before applying them to other groups. Christen et al., 2014.

12. Immunity, energy and mood

Vitamin C, vitamin D and zinc contribute to normal immune function, but additional supplementation has not been shown to boost immunity reliably in people with adequate intake. Small trials have reported changes in nutrient biomarkers or self-reported illness, but these do not establish robust protection against infection. B vitamins support energy metabolism; correcting a deficiency can help deficiency-related fatigue, whereas multivitamins are not proven energy boosters for well-nourished adults. They are not established treatments for depression or anxiety. Persistent fatigue, mood symptoms or cognitive decline warrants appropriate clinical assessment.

13. Australian pregnancy guidance: folic acid, iodine and vitamin A

Australian recommendations focus on specific nutrients rather than assuming an ordinary multivitamin is suitable. Guidance generally recommends 400 micrograms of folic acid daily when planning pregnancy and through the first 12 weeks; some people need higher clinician-directed doses. An iodine supplement containing 150 micrograms daily is commonly recommended when planning pregnancy, during pregnancy and breastfeeding, subject to individual circumstances. Excess preformed vitamin A (retinol) can harm fetal development; iron needs require individual assessment. Pregnancy-specific formulations are preferable to assuming an everyday adult multivitamin provides appropriate nutrition.

Nutrient	General Australian guidance
Folic acid	400 micrograms daily before conception and during early pregnancy, unless higher dose advised
Iodine	Generally 150 micrograms daily as a supplement, subject to clinical circumstances
Preformed vitamin A	Avoid excessive doses
Iron	Assess individual need

14. Safety: when multivitamins can cause problems

Standard-dose products are usually well tolerated, but safety depends on formulation and combined intake. Excess supplemental vitamin B6 may cause peripheral neuropathy; too much preformed vitamin A can cause toxicity and is especially concerning in pregnancy; excessive iron is harmful and iron-containing tablets must be secured away from children. High-dose beta-carotene supplements increased lung cancer risk in certain trials among smokers and other high-risk populations. Vitamin K may interfere with warfarin therapy, and minerals such as calcium and iron can affect absorption of some medicines. A multivitamin, fortified food, magnesium tablet and protein supplement may provide overlapping nutrients. More is not necessarily better.

15. Who may benefit from a multivitamin?

A supplement may have a practical role where there is inadequate dietary intake, a restricted diet, limited food access, particular life-stage requirements or a documented deficiency. Older adults may benefit from improved nutrient intake, while COSMOS suggests a modest cognitive-test advantage, not proven dementia prevention. Pregnancy calls for targeted folic acid and iodine guidance. Diagnosed deficiencies may require higher-dose or targeted therapy under medical advice.

Situation	Approach
Restricted diet	Match product to likely shortfalls
Older adults	Assess diet and clinical needs; cognitive outcomes remain uncertain
Pregnancy planning	Use pregnancy-specific nutrient guidance
Documented deficiency	Use targeted treatment where needed
Healthy adult with adequate intake	No established general disease-prevention benefit

16. Australia and the United States: what differs?

American trials provide much of the strongest disease-outcome evidence, while Australian readers should account for local food fortification, nutrient intake, supplement regulation and pregnancy advice. Australia regulates many complementary medicines through the Therapeutic Goods Administration; US dietary supplements operate under the FDA framework. Neither regulatory system means that every broad marketing claim about a multivitamin has been established by a large randomised trial.

17. How to choose a multivitamin

Identify the actual dietary or medical need. Read the ingredients and doses rather than assuming more is better. Consider nutrients from fortified foods and other supplements, and choose a formulation appropriate to your age, pregnancy status, diet and medical conditions. Review interactions with a pharmacist when taking prescription medicines. Prioritise food quality: a tablet cannot reproduce the full benefits of a varied diet.

18. Frequently asked questions

Is taking a daily multivitamin worth it?

It may help if your diet is low in nutrients it provides. Broad disease prevention has not been established in healthy, adequately nourished adults.

Do multivitamins improve memory?

COSMOS reported modest improvements in older adults’ cognitive test scores, but meaningful long-term clinical benefit remains uncertain.

Can they prevent dementia?

There is no convincing trial evidence that they prevent dementia.

Do they prevent cancer?

Cancer trial results are mixed and do not support routine use specifically to prevent cancer.

Will I live longer?

No reliable longevity benefit has been demonstrated.

Are they safe?

Standard doses are usually well tolerated, but excess nutrients and medicine interactions can cause problems.

Should I take an ordinary multivitamin during pregnancy?

Seek advice on folic acid, iodine and an appropriate prenatal formulation.

19. Bottom line

The strongest reason to take a multivitamin is to address a genuine dietary or nutritional shortfall. American trials suggest small improvements on certain memory tests in older adults but no established dementia prevention. Major studies have not demonstrated cardiovascular protection or longer life, and cancer results conflict. For Australians, the useful question is whether a specific product supplies nutrients you actually need without excessive doses. A GP, accredited practising dietitian or pharmacist can help evaluate your diet, medicines and health circumstances. This article is general information, not personal medical advice.

Daily Multivitamins: Do They Make You Healthier? What the Evidence Says