Nutritionist's Note: What Is a Health-Care Threshold?
Does a supplement do nothing if you don't take enough of it?
Why does an adequate dose matter?
Supplements don't work simply because they're taken — they work when taken in sufficient amounts. For a noticeable health benefit, the concentration of the nutrient in the body must exceed a threshold and reach an "effective health-care concentration".
[Nutrient concentration in the body + steady accumulation (daily intake > daily consumption)] > health-care threshold → effective concentration
Every day an animal consumes not only protein, fat and carbohydrate for energy, but also a range of vitamins and minerals to keep body functions in good order.
If the current concentration in the body is below the threshold, daily intake must exceed daily consumption, and be sustained over time, gradually raising the level until it passes the threshold — only then does a significant benefit appear.
More precisely, what matters is the accumulated concentration in the target tissue. Take the familiar example of human eye care: the concentration of lutein in the macula.
The body uses lutein daily for basic physiology and antioxidant defence (daily consumption). To reach an effective concentration you need enough lutein every day (intake > consumption), sustained for several months, before macular lutein rises past the threshold and delivers significant eye protection.
Remember this principle: the target tissue must accumulate a high enough concentration before there is a noticeable benefit.
Lutein reaches the macula slowly via the blood, so a steady intake is needed to keep enough lutein in the blood to be delivered. After ingestion, blood lutein rises quickly; the macula absorbs it slowly, so its concentration climbs more gradually (Figure 1).
Research also shows that when people stop taking lutein, more than half of the increase in blood lutein is lost within two days — while the macula keeps rising slowly and holds a stable level for some time (Figure 2).
Whatever the nutrient, however, levels eventually fall back to baseline and the benefit is lost. Long-term, steady intake through the daily diet is therefore the best approach.
The threshold concept applies to animals as well as humans, and to many nutrients — glucosamine and chondroitin, for example — though each nutrient behaves differently in the body, needs a different amount (threshold), and individuals vary further still.
In short: steady, long-term intake of health-care nutrients, so that the target tissue accumulates a concentration above the threshold, is what works.
References
- Xiong K, et al. Dose-Response Relationship Between Oral Lutein Intake and Plasma Lutein Concentration: A Randomized Controlled Trial. Front Nutr. 2022;9:924997.
- Gupta RC, et al. Comparative therapeutic efficacy and safety of type-II collagen (UC-II), glucosamine and chondroitin in arthritic dogs: pain evaluation by ground force plate. J Anim Physiol Anim Nutr. 2012;96(5):770-7.
- Chen Y-S. Eye-care prescriptions from an ophthalmology authority (Chinese). 2017.
