Experts say that the best time to take iron, vitamin D, and B12 supplements depends more on what you eat, drink, and take for other medications than on a specific time of day. A review of 84 studies found that for generally healthy adults, taking routine vitamin and mineral supplements does not significantly lower the risk of heart disease, cancer, or early death. In some cases, taking these supplements without a clear need could even be harmful. For example, high doses of certain water-soluble vitamins, like B6, can damage nerves, and too much vitamin A can cause toxicity. There are specific, evidence-based reasons to take supplements. These include taking folic acid before and during early pregnancy, vitamin B12 for people who cannot get enough from food, and vitamin D supplements during autumn and winter, as recommended by UK health guidelines. A diagnosed deficiency is another valid reason. However, it is important not to take supplements simply based on vague symptoms, like fatigue, without consulting a healthcare provider. Iron supplements are used to treat iron deficiency anemia, and their effectiveness depends on how and when they are taken. For instance, drinking coffee with an iron supplement can reduce absorption by nearly half. A study found that taking a 100mg iron supplement with coffee reduced absorption by 54%, compared to taking it with water. Even taking the supplement with breakfast, which included orange juice, reduced absorption by 66%. However, adding 80mg of vitamin C increased iron absorption by 30%, and more vitamin C did not offer additional benefits. The study also found that iron absorption was 37% lower in the afternoon than in the morning, though this difference was not statistically significant. Vitamin D, which is fat-soluble, is better absorbed when taken with a meal containing fat. A randomized study found that vitamin D3 was absorbed more effectively with a fatty meal than with a fat-free one. This suggests taking vitamin D with a main meal is beneficial. However, the study did not compare breakfast with dinner. Certain medications, such as orlistat and corticosteroids like prednisolone, can affect how the body processes vitamin D. Adjusting the time of intake may not resolve these issues, and it is advised to continue prescribed medications while consulting a healthcare professional about vitamin D levels. Vitamin B12 is essential for red blood cell production and the nervous system, and is found in animal-derived foods and fortified products. Vegans who do not take supplements tend to have poorer B12 status than those who consume animal products. Supplements can improve B12 levels in such cases. However, the time of day is less important than the reason for taking B12. Medications like metformin and acid-suppressing drugs such as omeprazole can reduce B12 absorption. Separating the doses may not be enough to counteract this. The NHS recommends taking prescribed cyanocobalamin tablets on an empty stomach, while over-the-counter products should follow the packet instructions. For those with absorption issues, high-dose tablets or injections may be needed. A review of clinical trials found limited evidence that high-dose oral B12 and injections had similar short-term effects, so treatment should be based on the underlying cause, symptoms, and medical advice. Before starting any supplement, it is important to determine whether there is an evidence-based reason to take it and whether the dose is appropriate. Check for overlapping ingredients in other products, such as multivitamins, energy drinks, or wellness powders. If using prescribed medications, consult a pharmacist about possible interactions and timing. For some supplements, the meal or drink taken with them can affect absorption. If no specific timing is needed, follow the recommended dose and instructions at a time that is easy to remember.