Supplement timing guides
Short, sourced answers. Every rule is graded by the evidence behind it.
When to take magnesium: morning or night?
Any time of day you will remember. The popular rule that magnesium must be taken at night has weak evidence; taking it consistently matters more than the clock. If you also take iron, keep them apart.
weakBest time to take creatine (and does it matter?)
Taking creatine every day matters most (graded moderate). Timing effects are small and uncertain (weak); some data slightly favour taking it around or after training.
moderateCan you take iron and calcium together?
Better not. Calcium taken with an iron meal or dose lowers how much iron you absorb (graded strong). Take them at different times of day. The exact 2-hour gap often quoted has not itself been tested.
strongWhen to take vitamin D: with food or without?
With a meal that contains some fat. Older adults absorbed more vitamin D3 when they took it with a fat-containing meal than with a fat-free one (graded moderate). Time of day itself matters less.
moderateCollagen timing: when to take marine collagen
Our protocol is marine collagen only: 5 g fasted in the morning, 15 g about 30-60 minutes before training, and an optional dose about an hour before bed. Timing evidence is limited, so every part is graded weak.
weakFish oil: morning or night?
The time of day matters less than the meal. Fish oil is absorbed better alongside a meal that contains fat (graded moderate), so take it with your fattiest meal, morning or night.
moderateZinc and iron: can you take them together?
Keep them apart where you can, as a precaution (graded weak). Iron reduced zinc absorption in solution, but not clearly when taken with meals.
weakAshwagandha timing: morning or night?
Follow your product label. Timing evidence for ashwagandha is limited, so no time of day is proven better (graded weak). If you take a prescription medicine, check with your doctor or pharmacist first.
weakCoffee and iron: how long to wait?
Avoid coffee or tea with your iron and in the 1-2 hours after it: they lower how much iron you absorb (graded strong). Coffee at least 1 hour before iron seems fine, but that rests on one study (graded weak).
strongHow long before bed should you stop caffeine?
At least 6 hours. In a sleep-lab study, caffeine taken 6 hours before bed still cut sleep by about an hour (graded moderate). For training, it works best 30-60 minutes before exercise.
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