When to Take Your Supplements (Chronobiology)

Written by Dr Jatin Joshi, co-founder and Chief Medical and Scientific Officer of Personally, and a researcher at the University of Oxford's Centre for Evidence-Based Medicine. I have a financial stake in this company, and you should weigh what follows with that in mind.

This question gets asked more than almost any other, and it usually gets answered badly, either with a shrug or with an elaborate schedule that nobody could keep for a fortnight.

The truthful answer has a shape to it. A handful of timing rules are real and worth following. A few more are plausible but thinly evidenced. Everything else is noise, and the single thing that matters more than all of it is whether you actually take the stuff.

Here is the ranking, most useful first.

Fat-soluble vitamins want a meal with fat in it. Vitamins A, D, E and K are absorbed alongside dietary fat, so taking them with a meal that contains some is measurably better than taking them with black coffee. It does not need to be a large amount of fat, and it does not need to be a particular meal. It needs to be food.

Some minerals compete with each other. Calcium taken at the same time as iron reduces how much iron you absorb. Zinc and copper compete for the same absorption route, and a large intake of zinc over a long period can lower copper. This is one of the genuine reasons to spread minerals across the day rather than taking everything at once, and it is one of the reasons a formula worth its salt does not simply pile every mineral into a single serving.

Iron is the fussy one. It is absorbed better away from food, and vitamin C taken with it helps with the plant form of iron. It also causes stomach upset in a lot of people when taken on an empty stomach, which is why so many people give up on it. If you are supplementing iron, it should be because a blood test showed you needed it, and how to take it is a conversation worth having with whoever ordered that test.

Anything stimulating belongs in the first half of the day. Green tea extract, guarana and similar botanicals carry caffeine. Caffeine has a long half-life, and in many people an afternoon dose is still doing something at bedtime. If your evening sleep is not what it was, look at what you are taking after lunch before you look at anything else.

Magnesium in the evening. You will read everywhere that magnesium should be taken at night. The reasoning is not unreasonable, and plenty of people prefer it that way. What I would not claim is that the timing itself has been well tested in humans. If evening suits you, take it in the evening. Do not believe anyone who tells you the hour is doing the heavy lifting.

Probiotics on an empty stomach, or with food. Both are argued, with sensible mechanisms on each side, and the honest position is that it depends on the specific strain and the specific product, and that for most people the difference is small.

Splitting doses through the day. For some nutrients there is a real argument that smaller amounts more often are better used. For most, at the amounts people actually take, it makes very little difference and adds a lot of admin.

Consistency. Comfortably, unglamorously, consistency.

A supplement taken at a slightly suboptimal time every day beats a perfectly timed one you manage four times a week. The gap between those two is far larger than the gap between the best and worst timing of the same product. So the practical advice is to attach it to something you already do without thinking, breakfast, brushing your teeth, making the coffee, and stop optimising after that.

If you have been carrying a mental spreadsheet of what to take when, you can put it down. Keep the four rules above. Let the rest go.

Ours ships as two servings a day, and the reason is the section above rather than anything more elaborate. Some of what a formula contains is better away from other things, some of it belongs at the stimulating end of the day, and some of it does not. Splitting the serving is how you get the separations that genuinely matter without asking anyone to run a timetable.