NATURTREU Sonnenfreund in the check: Vitamin D3 & K2 drops (1,000 IU)

Overview

The ingredients that count

Vitamin D and glucose metabolism

Observational studies show clearly: low vitamin D levels go along with a higher diabetes risk . For a long time, the hope was derived from this that supplementation protects.

The large D2d study (Pittas et al., NEJM 2019) tested this: in people with prediabetes, high-dose vitamin D did not significantly lower diabetes risk compared with placebo. Later analyses suggest that people with a very low baseline level might benefit .

My conclusion: vitamin D is important – for bones and the immune system there are authorised claims and good research . As a blood-sugar intervention it did not prove itself in the best available study. Correcting a deficiency: yes. Expecting a metabolic effect: no.

Why K2 alongside?

Vitamin K2 is combined because it is said to support the deposition of calcium in bones rather than vessel walls. There is a plausible rationale for the combination; the research for the additional benefit is moderate .

Points to consider

Vitamin D is fat-soluble and can be overdosed. The level should be measured before high-dose intake. Vitamin K2 is problematic when taking vitamin K antagonists (e.g. warfarin) – clarify medically without fail.

Test idea

No CGM test; instead laboratory value (25-OH vitamin D) before and after the dark season.

All of my own measurements are labelled as a single-case observation (n=1) and cannot be transferred to other people.

Sources

1. Product information NATURTREU Sonnenfreund: composition and dosage per manufacturer (as of July 2026).
2. EU Register of authorised health claims, Regulation (EC) No 1924/2006.
3. Specialist literature and meta-analyses on the ingredients mentioned; classification by assessment in the text.
4. Lean MEJ et al.: DiRECT trial on remission in type 2 diabetes through weight management, The Lancet.