Vitamin supplements: which ones work, which ones waste money, and which can cause harm

Do supplements work for most people?

The honest answer for healthy adults eating a varied diet is: usually not. Multiple large randomised controlled trials, including studies involving tens of thousands of participants followed for years, have consistently found that daily multivitamins do not reduce the risk of cardiovascular disease, cancer, cognitive decline or early death in people who are not deficient in anything. The supplement industry is large and profitable, and the marketing is persuasive, but the evidence base for routine supplementation in healthy people is weak.

What does work is targeted supplementation for people who have a demonstrated deficiency or a well-defined increased need. Pregnant women need folic acid. People with limited sun exposure or who wear full covering in hot countries often need vitamin D. People who have had certain surgeries, who follow a strict vegan diet, or who have malabsorption conditions may genuinely need B12, iron or other specific nutrients. The question is always whether you are in a group that needs something, not whether the supplement is marketed to you.

This matters particularly in the Arab world, where self-prescribing is common, pharmacy access is easy and supplements are sold at relatively low cost compared to a doctor visit. It is easy to spend money on things that do not help, and it is possible, with some vitamins, to take enough to cause harm.

Why is vitamin D deficiency so common in sunny countries?

This surprises many people, and it is worth explaining carefully. Vitamin D is synthesised in the skin when ultraviolet B radiation from sunlight hits it. The Middle East and North Africa receive enormous amounts of sunlight. And yet a 2018 review published in Bone Reports, covering studies across the region, found vitamin D deficiency rates of 30 to 90 percent in various populations, with women, older adults and people who cover their skin for religious or cultural reasons at highest risk.

There are several reasons for this apparent paradox. Extreme summer heat keeps people indoors during the hours when UVB radiation is strongest, typically 10am to 3pm. When people do go outside, they often use high-factor sun protection, which blocks UVB effectively. Dark skin requires more sun exposure to produce the same amount of vitamin D as lighter skin, and many Arab and South Asian populations in the region have darker skin. In addition, traditional covering garments, worn by a significant proportion of women across the region, block most skin from the sun entirely.

A 2018 study specifically looking at Arab women in early pregnancy found deficiency rates that were alarming, and this matters because vitamin D plays a role in bone development in the growing baby, immune function and several other processes. Deficiency during pregnancy has been associated with a higher risk of pre-eclampsia and low birth weight. Supplementation during pregnancy is recommended in international guidelines and is safe when kept within normal therapeutic doses.

Folic acid in pregnancy: the one supplement with the clearest evidence

Folic acid (vitamin B9) before and in the first weeks of pregnancy is not optional: it is the single best-evidenced supplement in obstetric medicine. Neural tube defects, which affect the brain and spinal cord of the developing baby, occur in the first four weeks after conception, often before a woman even knows she is pregnant. Adequate folic acid in the months before conception and through the first trimester reduces the risk of these defects by around 70 percent.

Awareness of this is lower than it should be in parts of the Arab world. A study published in Annales de Genetique looked at folic acid awareness in an Arab community with a high rate of consanguineous marriage (marriage between relatives), which itself raises the risk of certain genetic conditions, and found that knowledge of folic acid supplementation before pregnancy was poor. This is a solvable problem: the supplement is cheap, the evidence is overwhelming, and the benefit is concentrated in the weeks when it is hardest to intervene after the fact.

The standard recommendation is 400 micrograms per day, ideally starting one to three months before trying to conceive and continuing through the first twelve weeks. Women who have previously had a baby with a neural tube defect, or who are taking certain anti-epileptic medicines, need a higher dose and should take this under medical advice. Folic acid at standard doses has no known harmful effects.

When vitamin A becomes dangerous

Vitamin A is essential. It plays a critical role in vision, immune function and the growth of cells throughout the body. True vitamin A deficiency, which is rare in urban populations with access to a varied diet, causes night blindness and serious immune problems. Where it does occur, in some rural or food-insecure settings, supplementation is an important public health intervention.

The danger that most urban Arab consumers face is the opposite: too much vitamin A from supplements. Unlike water-soluble vitamins such as C and the B vitamins, vitamin A is fat-soluble and accumulates in the body. High doses taken over weeks or months cause a condition called hypervitaminosis A (vitamin A excess), the symptoms of which include severe headache, nausea, liver damage, bone pain, and dry and peeling skin. A 2026 systematic review in Clinica Chimica Acta examined the clinical spectrum of vitamin A toxicity and found that it is frequently misdiagnosed because the symptoms mimic several other conditions.

The critical safety point is that vitamin A is often present in multivitamins, in cod liver oil, and in skin supplements sold in pharmacies. Taking several products simultaneously can push total daily intake well above the safe upper limit. Pregnant women are at particular risk: doses above 3,000 micrograms (10,000 IU) per day can cause fetal malformations. Pregnant women should avoid high-dose vitamin A supplements entirely and should check whether any multivitamin they take contains retinol.

Vitamin D: too much is also a problem

Vitamin D deficiency is common and worth treating, but the solution is not to take the largest dose available. Vitamin D toxicity (hypervitaminosis D) is real, though less common than vitamin A toxicity, and it happens when people take very high doses, typically above 4,000 IU per day over extended periods, without monitoring their blood levels. The problem is that many high-dose vitamin D preparations are sold in pharmacies throughout the Gulf and the Levant at strengths of 50,000 IU per capsule, which are genuinely medical doses intended to be taken weekly or monthly under supervision, not daily.

Vitamin D toxicity causes hypercalcaemia (high calcium in the blood), the symptoms of which are nausea, excessive thirst and urination, confusion, kidney pain and, in severe cases, kidney stones. The treatment involves stopping supplementation and, in serious cases, hospitalisation. The point here is not to discourage supplementation but to say that the dose matters, and that someone who takes a 50,000 IU capsule every day because more seems better is taking a dangerous amount.

The right approach is to check your blood level first. The test is a simple and inexpensive blood draw for 25-hydroxy vitamin D. If you are deficient, a doctor or pharmacist can recommend an appropriate replacement dose. If you are not, you may not need to supplement at all, or a low maintenance dose may be appropriate. Treating a number you actually know is almost always better than supplementing based on a guess.

Iron: only supplement if you actually have deficiency

Iron deficiency anaemia is extremely common among women in the Arab world, particularly in women of reproductive age who menstruate heavily, and in pregnant women. The appropriate response to confirmed iron deficiency is supplementation, and iron supplements are effective. The problem arises when people take iron supplements without a confirmed diagnosis.

Iron is not harmless in excess. Taking iron supplements when you do not need them can cause constipation, nausea and stomach pain in the short term, and long-term high iron intake has been associated with oxidative stress and, in people with a genetic condition called haemochromatosis, serious liver damage. Men and post-menopausal women rarely need iron supplements and should not take them without a blood test showing iron or ferritin levels are low.

If you are a woman who feels chronically tired, pale or breathless, ask for a full blood count and a ferritin level before buying iron supplements. Low ferritin with a normal haemoglobin is called iron deficiency without anaemia and still benefits from supplementation. A normal ferritin means iron is probably not your problem, and investigating other causes, including thyroid function and vitamin D, will be more productive.

Zinc, omega-3 and supplements for immunity

Zinc does have a genuine role in immune function. A 2017 paper in the journal Nutrients reviewed the biochemistry in detail and confirmed that zinc is essential for the development and function of immune cells. Zinc deficiency impairs immunity and increases susceptibility to infection. The question is whether people without deficiency benefit from supplementation, and the answer is generally no. Zinc supplements at moderate doses are safe, but very high zinc intake suppresses copper absorption and can itself cause immune problems.

Omega-3 fatty acids, found naturally in oily fish, walnuts and flaxseed, have strong evidence for specific uses: high-dose prescription omega-3 (icosapentaenoic acid and docosahexaenoic acid at doses of 2 to 4 grams per day) reduces triglycerides in people with hypertriglyceridaemia. The evidence for lower-dose over-the-counter fish oil for general heart health in low-risk people is much weaker than the marketing suggests.

The honest summary for most supplements marketed as immunity boosters is that they will not prevent you catching a cold if you are not deficient in anything, and the immune system does not benefit from megadoses of micronutrients. A varied diet containing fish, pulses, nuts, vegetables and fermented dairy provides the micronutrient base that the immune system actually needs. Supplements fill gaps; they do not build on top of an already replete system.

How to decide what you actually need

The most rational starting point is not a pharmacy shelf but a blood test. A basic panel covering 25-hydroxy vitamin D, a full blood count, ferritin, and B12 if you eat little or no meat will tell you whether you have any actual deficiencies. If you do, supplementation is warranted and targeted. If you do not, a multivitamin is unlikely to benefit you and may, with some nutrients, cause harm if doses are high.

Some people have clear indications regardless of a blood test: women planning pregnancy should take folic acid, women who are veiled or spend little time in the sun should strongly consider vitamin D, vegans and strict vegetarians should take B12 regularly. Beyond these clear cases, the decision is best made with a doctor or qualified dietitian rather than based on marketing or social media recommendations.

In Arab countries, pharmacists are often the first point of health contact and are frequently knowledgeable. A good pharmacist will ask about your diet, your situation and any medicines you take before recommending a supplement. If you are offered a recommendation without those questions, it is worth seeking a second opinion from a doctor before spending money.

Sources

• Chakhtoura M, Rahme M, Chamoun N et al: Vitamin D in the Middle East and North Africa, Bone reports, 2018
• Pludowski P, Holick MF, Grant WB et al: Vitamin D supplementation guidelines, The Journal of steroid biochemistry and molecular biology, 2018
• Daley SF, Goyal A: Vitamin A Toxicity, 2026
• Padmakar S: Clinical Spectrum and Management of Hypervitaminosis A: A Systematic Review of Case-Based Evidence, Clinica chimica acta; international journal of clinical chemistry, 2026
• Al-Musharaf S, Fouda MA, Turkestani IZ et al: Vitamin D Deficiency Prevalence and Predictors in Early Pregnancy among Arab Women, Nutrients, 2018
• Jaber L, Karim IA, Jawdat AM et al: Awareness of folic acid for prevention of neural tube defects in a community with high prevalence of consanguineous marriages, Annales de genetique, 2004
• Wessels I, Maywald M, Rink L et al: Zinc as a Gatekeeper of Immune Function, Nutrients, 2017