Supplements: what the evidence actually supports

Supplements are a large industry built on a reasonable idea: if a nutrient is essential, more of it should be better. For a few specific situations that holds. For most people taking most products, it does not — and a supplement is not automatically safe simply because it is available without a prescription.

Where the evidence is genuinely good

• Vitamin D. At Canadian latitudes the skin makes little or none through the winter months. Health Canada recommends a daily supplement for adults over 50, and many people benefit year-round — particularly those with darker skin, limited sun exposure, or who cover up outdoors.
• Folic acid before and during early pregnancy. Substantially reduces the risk of neural tube defects. Because it works in the first weeks, often before a pregnancy is known, it is advised for anyone who could become pregnant.
• Vitamin B12 for people eating little or no animal food, and for many adults over 50, who absorb it less efficiently. Deficiency causes nerve damage that is not always reversible.
• Iron, when a blood test shows you need it. Iron deficiency is common, especially with heavy periods. It should be confirmed by testing, not assumed — excess iron is harmful.
• Calcium, if your diet falls short and you are at risk of osteoporosis. Food first where possible.

Where it is weaker than the marketing suggests

Multivitamins have not been shown to prevent heart disease or cancer in well-nourished people. High-dose antioxidant supplements have performed poorly in trials, and some have caused harm. "Immune boosting" is not a recognised mechanism — the goal is a functioning immune system, not an overactive one.

Three practical cautions

1. Interactions are real. St John's wort reduces the effect of a long list of prescription medicines, including some antidepressants and birth control. High-dose vitamin K affects warfarin. Tell every prescriber what you take, including anything "natural".
2. More is not better, particularly for the fat-soluble vitamins A, D, E and K, which accumulate. Toxicity is uncommon but it does happen, usually through high-dose products.
3. Check the licence. In Canada, a legally sold natural health product carries an NPN or DIN-HM number on the label. It means Health Canada has reviewed the product for safety, evidence and quality. A product without one has not been through that.

A sensible approach

Be clear about what you are trying to fix. If it is a deficiency, ask for a blood test rather than guessing — supplementing blindly can mask a problem worth finding. If it is a symptom such as fatigue, low mood or poor sleep, those have causes worth investigating properly, and a supplement can delay that.

A registered dietitian can review your actual diet and tell you what, if anything, is missing. A naturopathic doctor registered with the College of Naturopaths of Ontario can advise on natural health products and is trained to check for interactions — worth asking about explicitly if you take prescription medication.

Sources

• Health Canada — Natural health products
• Health Canada — Vitamin D
• Health Canada — Folic acid and pregnancy
• Dietitians of Canada — Supplements