Supplements on suspicion

The watering-can principle

Supplementing without a blood analysis is like watering a plant without knowing whether it needs water. Sounds harmless. The consequences are not always.

A ferritin of 120 ng/mL plus an iron supplement loads the body for no reason. A vitamin D level of 70 ng/mL plus another 4,000 IU a day adds no measurable benefit. And anyone taking magnesium while the real bottleneck is zinc is turning the wrong dial.

In clinical practice the pattern repeats: of five supplements a patient brings in, two make sense, one is superfluous, and two are missing entirely. Money spent on products with no effect, while the actual gaps stay untreated.

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What the research shows

The evidence on targeted versus untargeted supplementation is unambiguous.

Vaucher et al. (2012) [1] studied 198 women with non-anaemic iron deficiency in a randomised, placebo-controlled trial. Result: only in women with ferritin below 50 µg/L did iron supplementation reduce fatigue by 47.7 percent. Placebo: 28.8 percent. In women without a deficiency: no difference versus placebo. The supplement had an effect only where a deficit was documented.

Levy et al. (2021) [2] analysed the vitamin D response in 1,300 women in a large randomised trial. Central finding: 70 to 79 percent of the individual response depends on baseline value and dose. Two women on the same supplementation protocol react completely differently. Blanket advice such as "1,000 IU of vitamin D for everyone" is therefore not scientifically tenable.

Slow et al. (2020) [3] identified genetic variants in the GC gene in 313 participants that significantly influence vitamin D response. Certain genotypes are biologically poor responders. For those people a standard dose is not enough, regardless of how faithfully they take it. Anyone who has been taking vitamin D for months and barely sees movement in their vitamin D level may simply be genetically different.

Conclusion: without knowing individual baseline values, every supplementation is an uncontrolled experiment. Why many women have symptoms despite "normal" lab values is covered in Your values are all normal.

What the aescolab data show

Real blood analyses confirm the study picture. The figures below come from aescolab client analyses and show how often relevant biomarkers sit outside the functional optimum.

Vitamin D: standard reference 30 to 100 ng/mL, functional optimum 50 to 80 ng/mL. In aescolab analyses, 75.7% of clients sit below the functional optimum. The difference between 35 and 60 ng/mL is clinically relevant, even when both sit "in range".

Ferritin: standard reference 15 to 220 ng/mL, functional optimum 50 to 130 ng/mL. 29.1% of clients sit below 50 ng/mL. A value of 20 is "normal" on a lab report and already advanced iron depletion in functional diagnostics. More in ferritin in women.

Omega-3 index: optimum 9 to 12 percent. 75.4% of clients sit below an index of 8%. One of the most frequently neglected markers, and one that diet alone rarely pushes into the optimal range. See the omega-3 index.

Magnesium: optimum 32 to 39 mg/L. Many values sit just under the threshold, but a standard lab report still flags them as "normal". Classic case: in range, not optimal.

Zinc: optimum 5.4 to 7.2 mg/L. Rarely included in a standard blood count, even though zinc is involved in more than 300 enzymatic processes.

At aescolab all of these markers are captured. Depending on panel depth, between 50 and 85+ biomarkers are determined in a single venous blood analysis.

The data-based approach

The alternative to the watering-can principle is a three-step process: measure, act, retest.

Step one: measure. A blood analysis that goes beyond GP standard, for example with an extended panel. Not only vitamin D and iron, but also zinc, magnesium and the omega-3 index.

Step two: act. Supplementation based on real values, not on social media. Targeted, not watering-can. Only what the body actually needs.

Step three: retest. Measure again after eight to twelve weeks. That is the only way to verify whether supplementation is having an effect, whether the dose is right, and whether the body is a responder - or whether an adjustment is needed.

Frequently asked questions on supplements

Can too much vitamin D be harmful?

Yes. Vitamin D is fat-soluble and stored in the body. Persistently high doses without monitoring can lead to hypercalcaemia. Hence: measure first, then dose, then retest.

Is a standard blood count at the GP enough?

For a first overview, yes. But ferritin, zinc and the omega-3 index are often not included. Those are exactly the values that separate "normal" from optimal. An extended panel closes that gap.

Should I stop all supplements until I have measured?

Not necessarily. But the values are only meaningful if what was taken beforehand is documented. Best practice: write down which supplements you take, and at which dose, before the blood draw.

How do I find the right dose?

The right dose is always individual. It depends on the baseline value, body weight, genetics and interactions with other nutrients. The Levy study [2] shows: same dose, different results. Only a blood analysis shows where you actually stand.

I have been taking supplements for months and still feel tired. Why?

That is a pattern we see often. You supplement diligently, but without a data basis. The dose may not fit, a nutrient you are not watching may be missing, or the bottleneck sits elsewhere (thyroid, inflammation markers). aescolab analyses up to 85+ biomarkers in a venous blood analysis and shows in the report which levers are actually relevant.

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Study references

1. Vaucher P, et al. Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin. CMAJ. 2012;184(11):1247-54. PMID: 22777991. DOI: 10.1503/cmaj.110950
2. Levy AP, et al. Vitamin D supplementation dose-response in VITAL. Am J Clin Nutr. 2021;113(2):440-449. PMID: 33471041. DOI: 10.1093/ajhp/zxaa424
3. Slow S, et al. Effect of adjunctive high-dose vitamin D3 in vitamin D deficient adults. Intern Med J. 2020;50(10):1267-1272. PMID: 31758650. DOI: 10.1111/liv.14306