I recently stopped taking all my supplements 3 weeks ago. Question: To be safe and make sure all these supplements are no longer in my system, how long should I wait?
Short answer: that's probably long enough.
once I re-introduce the supplements, one by one, how long should I wait to make sure that supplement is fully in my system?
Short answer: 8 weeks or so. See long answer.
The term "wash-out period" generally refers to a (foreign) substance being entirely eliminated from the body. But nutrients cannot be eliminated from the body or you will risk developing a disease. Nonetheless, dietary supplement research does sometimes employ a "wash-out period," although I've never been fully satisfied with the rigor of most wash-out periods.
Here's one example of the length of a wash-out period used in peer-reviewed research:
Beneficial effects of a soy-based dietary supplement on lipid levels and cardiovascular risk markers in type 2 diabetic subjects - PubMed
Research design and methods: Twenty type 2 diabetic subjects participated in a crossover trial. They were randomized to double-blind supplementation for 6 weeks with Abalon (soy protein [50 g/day] with high levels of isoflavones [minimum 165 mg/day] and cotyledon fiber [20 g/day]) or placebo (casein [50 g/day] and cellulose [20 g/day]), separated by a 3-week wash-out period.
Here's another study example:
Vitamin K–containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7 | Blood | American Society of Hematology
For single dose-response they used:
Each single dose was followed by a 2-week wash-out period before increasingly higher doses were administered.
For prolonged intake the researchers used:
Eighteen volunteers were randomized to take 0.22 μmol/d of either K1 or MK-7 in a crossover design. The treatment with each vitamin was 6 weeks with a wash-out period of 12 weeks.
Determining a sufficient wash-out period could be complex. For example, vitamin B-12 can be stored in the liver for years. It is often reported to be stored for 2 to 4 years, but I have read cases where it was stored for more than ten years. In one case, the person ate a vitamin B-12 deficient diet for more than ten years before symptoms of B-12 deficiency actually showed up.
We know that fat soluble vitamins can generally be stored in the body longer than water soluble vitamins, but as the B-12 (water soluble) example shows, it's not always that simple. However, as a general rule, some fat soluble vitamins can also be stored in fat tissue for years (and potentially released when one diets to lose weight).
Having said all that, I would think a 3 week wash-out period would probably be sufficient for the kind of experiment you wish to do. That's only a guess due to the complexity described above.
Are the supplements you are testing all single-ingredient products? If not, that is another level of complexity. If any of the products you test have overlapping ingredients, you again have some complexity to deal with.
In my personal experiments to find supplements that produce desired result, I have not have good success testing supplements one-by-one. The best (and in my opinion, most scientific) way to test nutrients is to put together a synergistic, well-designed program of dietary supplements and test them as a unit. It generally requires a combination of nutrients to effectively manage blood pressure (and this is certainly true for intraocular pressure).
However, your goal is different. You wish to eliminate a supplement if it is producing an undesired side effect. That may be easier.
For this goal, I do have a suggestion that I think is more time efficient and more realistic for people who take a lot of supplements, given that testing one-by-one with long wash-out periods could make your experiment last many months or even a year+ (depending on how many supplements you need to test).
My suggestion is based on the binary search algorithm. It has a proven efficiency, and we can meet the requirements of the algorithm as long as you sort your supplements into a proper list.
The steps below are based on the fact that you have already done a 3 week wash-out period. (It can work without any prior wash-out period, but I might alter the steps slightly in that case, depending on the specifics.)
- Put your supplement list in a certain order based on ingredients. For example, any supplements that contain the same ingredient(s) need to be grouped together. Other than that, the order does not matter, except it cannot change once you begin this experiment.
- Divide your supplement list in half and be sure any supplements that contain the same ingredient(s) are not present in both halves of the list. If two of your supplements contain vitamin B-6, for example, never split them into different halves of your list.
- Take only the supplements in one half of your list for a sufficient period of time (say 8 weeks -- or until the unwanted effect appears, if sooner).
- Did the unwanted side effect appear? Yes or no?
- If yes, you have identified that there is a problem supplement in the half of the list you just tested. To identify which supplement is the problem, you now work with just this half of the list, but you start again at step 2 above. You divide this half in half once again and test it for the same number of weeks (e.g., 8). No additional washout period is required in this study design. You are simultaneously washing out half the items for X weeks or longer while testing the other half of the items, and repeating this. As you keep dividing the list in half, you get down to 2 supplements and finally to one. This algorithm is the most efficient way to find this one item in a sorted list.
- If no, you have proven that none of the supplements in this half of your list cause the unwanted effect. So in one single test, you were able to green-light half of your list. Now switch your attention to the other half of your list and repeat from step 3 above.