These three supplements appear on almost every "what to take" list in mainstream health content. They are often discussed as obvious choices — routine additions for anyone interested in health. The reality is more nuanced. The case for each is real but varies in quality, and the right approach is different for each compound. This article covers all three honestly.
Vitamin D
What it does. Vitamin D is a fat-soluble compound that functions more like a hormone than a vitamin. It regulates calcium and phosphorus absorption (essential for bone health), supports immune function, influences muscle function, and modulates hundreds of gene expressions involved in cellular maintenance.
Why deficiency is common. The body synthesises Vitamin D through sun exposure on skin — specifically from UVB radiation. The problem is that modern life creates significant barriers to adequate synthesis: indoor work, sunscreen use, high-latitude geography (including most of Australia's southern population in winter), darker skin tone (which reduces synthesis rate), and clothing that limits skin exposure. Dietary sources of Vitamin D are few and modest — fatty fish, eggs, and fortified foods contribute, but rarely enough to compensate for inadequate sun exposure.
Vitamin D insufficiency is widespread in Australia, particularly in winter in southern states. Studies across Australian populations consistently find that a significant proportion of adults have blood levels (25-OH Vitamin D) below the threshold associated with optimal function.
The case for supplementing. Unlike many supplements, the argument for Vitamin D is not primarily about performance outcomes — it's about ensuring adequacy in a nutrient that the modern environment makes difficult to obtain. The right approach starts with a blood test: a 25-OH Vitamin D measurement tells you your actual status. Below 50 nmol/L indicates deficiency; 50–75 nmol/L is insufficient; above 75 nmol/L is generally considered adequate. Supplementation dosing should be guided by this result — there is no value in supplementing aggressively if you're already sufficient, and inadequate supplementation won't close a meaningful deficiency.
Omega-3 (EPA and DHA)
What it does. Omega-3 fatty acids encompass several related compounds. The ones with the strongest evidence are EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), both long-chain fatty acids found in fatty fish and marine algae. They are incorporated into cell membranes throughout the body and have roles in inflammation regulation, cardiovascular function, and brain health.
ALA (alpha-linolenic acid) from plant sources — flaxseed, walnuts, chia seeds — is also an omega-3, but the conversion to EPA and DHA in the human body is inefficient (typically less than 10%). For practical purposes, EPA and DHA status depends on direct consumption of marine sources or supplementation.
The evidence. A 2021 meta-analysis of 63 randomised controlled trials found that omega-3 supplementation significantly reduced triglycerides, blood pressure, and markers of systemic inflammation. The cardiovascular evidence is reasonably strong, though the most meaningful effects are seen in people with existing risk factors or low baseline intake. For general populations with adequate dietary fish intake, supplementation adds less.
Where the gap usually is. Most Western diets are characterised by high omega-6 intake from processed foods and seed oils, and low omega-3 intake. This imbalance — sometimes described as an omega-6 to omega-3 ratio as high as 20:1 in some populations, against an historical range closer to 4:1 — may contribute to chronic low-grade inflammation. Dietary fish intake (2+ serves of fatty fish per week) is the most reliable way to address this. Supplementation is most relevant for people who don't eat fatty fish regularly.
What to look for on a label. Fish oil labels often lead with the total oil volume (1,000mg capsule) rather than the actual EPA+DHA content, which may be considerably lower. What matters is the combined EPA+DHA per serving, not the total oil weight. Aim for at least 500mg EPA+DHA per day; higher amounts (1–2g) are used in studies targeting specific health outcomes.
Magnesium
What it does. Magnesium is involved in over 300 enzymatic reactions, including muscle contraction, nerve signalling, protein synthesis, blood glucose regulation, and ATP production. It is the fourth most abundant mineral in the human body and is required for essentially every energy-producing process.
Why deficiency is common and under-detected. Dietary magnesium intake has declined significantly in many Western populations, partly due to modern agricultural practices that reduce mineral content in soil and therefore in food. The foods highest in magnesium — leafy greens, legumes, nuts, seeds, whole grains — are also the foods most underrepresented in typical Western diets.
Standard serum magnesium tests are misleading. Serum levels reflect only 1% of total body magnesium; the vast majority is inside cells and bone. The body prioritises maintaining serum levels within a narrow range, so serum magnesium can appear normal even when intracellular and total body status is inadequate. This makes standard blood tests an unreliable indicator of true magnesium status.
The evidence on supplementation. The research on magnesium supplementation is messier than for Vitamin D or creatine. There is evidence that supplementation improves sleep quality, reduces muscle cramps, and supports healthy blood pressure — but the effect sizes are modest and the studies are variable in quality. The most honest framing is that supplementing to close a dietary gap is likely beneficial even when the clinical evidence for specific outcomes is inconsistent.
Forms matter. Not all magnesium supplements are equal in bioavailability. Magnesium oxide — the cheapest and most common form — has poor absorption (around 4%). Magnesium citrate is better absorbed and widely available. Magnesium glycinate (magnesium bound to the amino acid glycine) is well-tolerated and has the best evidence for sleep applications. For most people starting supplementation, magnesium glycinate or citrate at 200–400mg per day is reasonable.