Foods Rich With Vitamin D

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Rapid, Economical Fluorescence Detection of Vitamin D in Selected Foods

This report provides results from fluorescence-emission experiments conducted by the Suarez Technology Group for the Weston A. Price Foundation. Fluorescence emission provides a relatively simple, low-cost method for identifying the presence and concentration of chemical compounds.

Certain compounds have intrinsic fluorescence—that is, they emit dif­ferent colors of light when excited by ultraviolet or visible light. The word intrinsic is used to emphasize the fact that the compound has this property entirely on its own; no additives or dyes are needed.

This “input-output color” relationship can be used to narrow down the chemical content of a substance, or provide clues on the pres­ence of a substance you’re looking for. The input-output relationship of fluorescence isn’t always unique, but it can be used to search for known substances or rule out the possibilities of others. While more costly and precise methods can be used,^1-7 fluorescence provides a first-step measure of confidence before investments are made into more detailed, precision testing.

In this study, fluorescence spectroscopy was used to detect the presence of vitamin D in seven foods: chicken liver, cod liver oil, lard, egg yolk, goose fat, Kerrygold butter, and grass-fed raw butter. Our primary goal was to detect the presence of vitamin D in these foods. Concen­tration levels—that is, amounts of vitamin D in each food—can also be inferred from the data, but we advise more precise controls before doing so.

A diagram of the experimental setup is shown in Figure 1. In each experiment, a small amount of each food was added to one milliliter of water, placed in a cuvette. These are referred to as samples. A 365-nm ultraviolet excitation signal was used in the setup—it can be thought of as the input signal. The input signal was provided to each sample, and—in the case of vitamin D—we expected to see an output signal around 380–390 nm.

The output signal is more properly called the fluorescence emission signal, and it is most easily observed at a 90-degree angle from the input signal. An optical filter isolated the wavelength band around 380 nm, since that was where we expected to see the vitamin D output signal. Using an optical fiber, the output signal was sent to a spectrometer. The spectrometer allowed the output signal data to be processed, stored and retrieved.

To have a reference for our experimen­tal data, before testing the seven foods, we examined the fluorescence of commercial, off-the-shelf vitamin D supplements. Those supplements contained known amounts of vi­tamin D, read directly from their labels. But, the supplements also contained MCT oil as an added ingredient. So, in order to distinguish the response of the MCT oil from the response of vitamin D, we first measured the response of commercial, off-the-shelf MCT oil supplements. The response of the MCT oil is shown in Figure 2.

 

We then measured the responses of the vitamin D supplements in various concentra­tions; these are shown in Figures 3–7. Observe that the general shape of the MCT oil’s output signal is significantly different from the output signals of the vitamin D supplements: the MCT oil’s output signal does not have a prominent intensity peak in the vicinity of 385 nm. This general shape of the output signal is called the fluorescence-emission response profile.

 

 

 

 

Next, we tested the seven foods. The results showed that they all exhibited fluorescence-emission response profiles similar to the vitamin D supplements, with the greatest intensity from pasture-raised lard. Again, notice that the pro­files shown in Figures 3–7 (vitamin D supple­ments) have a prominent intensity peak near 385 nm; this peak also appears in the profiles shown in Figures 8–14, which are the profiles of the seven foods. Details on the specific food and amount of the food used in each sample are provided in the caption of each figure.

 

 

CONCLUSIONS

These experimental results strongly sug­gest the presence of vitamin D in chicken liver, cod liver oil, pasture-fed lard, egg yolk, goose fat, Kerrygold butter and pasture-fed raw but­ter. This is because the fluorescence-emission response profiles we observed from the food samples closely resembled the response profiles of the vitamin D supplements.

These results warrant more detailed studies on the vitamin D content of these foods, with a focus on the amount of food content used in each sample and on the unique spectral signature of vitamin D. In this study, with the exception of the egg yolk, we restricted each sample to foods in liquid form, with no more than 0.5 mL of each food. The amount of each food added to each sample could not be measured with greater precision in this study. Also, other techniques such as Raman spectroscopy can be used to give even more compelling evidence of vitamin D content in these foods.

REFERENCES

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2. Sebbar E, Choukri M. Vitamin D status in the population of Eastern Morocco: study of vitamin D2 and vitamin D3 by high performance liquid chromatography. Mater Today Proc. 2023;72(7):3432-3434.
3. Vitamin D numbers: what they really mean. Quest Diagnostics, n.d. https://www.questdiagnostics.com/healthcare-professionals/about-our-tests/endocrine-disorders/vitamin-d-numbers
4. Delrue C, Speeckaert MM. Vitamin D and vitamin D-binding protein in health and disease. Int J Mol Sci. 2023 Feb 28;24(5):4642.
5. Lu M, Hollis BW, Carey VJ, et al. Determinants and measurement of neonatal vitamin D: overestimation of 25(OH)D in cord blood using CLIA assay technology. J Clin Endocrinol Metab. 2020 Apr 1;105(4):e1085–92.
6. Sa’aleek AA, Alshishani A, Shaghill L, et al. Determination of vitamin D3 in pharmaceutical products using salting-out assisted liquid-liquid extraction coupled with reversed phase liquid chromatography. Microchem J. 2023 0ct;193:109077.
7. Xu X, Jia C, Zhang F, et al. Sensitive and facile detection of vitamin D based on fluorescent labeled aptamer probe and exonuclease I-assisted signal amplification. J Fluoresc. 2025 Oct;35(10):9719-9729.

 

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