Thyroid and Nutritional Markers Panel

Total B12 measures all forms of cobalamin circulating in the blood, including forms bound to proteins that cells cannot easily access. Active B12 — holotranscobalamin — measures only the fraction that is bound to transcobalamin II and can be taken up by cells. Research shows that some individuals have adequate total B12 but low active B12, meaning their cells are functionally deficient despite a blood level that appears normal. Including both markers catches these cases that a total B12 alone would miss — particularly relevant for older adults, vegans, and those on medication that impairs B12 absorption.

Iron is a cofactor for thyroid peroxidase, the enzyme that produces thyroid hormones. When ferritin (iron stores) is low, the gland’s ability to synthesise T4 and T3 is compromised. Additionally, iron-containing proteins called iodothyronine deiodinases are responsible for converting T4 to the active T3 in peripheral tissues. Low ferritin therefore reduces both production and activation of thyroid hormones. Many people, particularly premenopausal women, have ferritin levels within the ‘normal’ laboratory range (typically above 12 ug/L) but below the 70 to 100 ug/L range considered optimal for thyroid function.

Vitamin D functions as an immune modulator, and vitamin D receptors are found throughout the immune system. Several studies have found that people with Hashimoto’s thyroiditis have significantly lower vitamin D levels than healthy controls, and that correcting deficiency can reduce TPO antibody titres. The relationship is not fully causal — vitamin D deficiency does not directly cause Hashimoto’s — but it appears to promote the autoimmune environment in which the condition thrives. Measuring vitamin D alongside antibodies helps identify whether optimising vitamin D status may be a useful adjunct to thyroid management.

People most likely to have nutritional deficiencies affecting thyroid function include: vegans and vegetarians (B12, ferritin), older adults over 60 (B12 absorption declines with age), those on metformin for diabetes (depletes B12), those on proton pump inhibitors long-term (impairs B12 and ferritin absorption), those with heavy menstrual periods (ferritin loss), and those in northern latitudes during winter months (vitamin D deficiency). The combined thyroid and nutrient data allows treatment to be directed at correctable causes rather than relying on levothyroxine dose adjustment alone.

Yes. Do not take your B12, iron, or vitamin D supplements on the morning of collection, as this can temporarily elevate these values and obscure true status. Biotin supplements should be paused for at least 48 hours before collection, as biotin interferes with thyroid assays. It is also advisable to test at the same time of year if monitoring vitamin D seasonally, since levels naturally fluctuate with sun exposure. Continuing other medications and supplements as normal is fine unless your GP has advised otherwise.

Your Trupoint Health report will include a narrative from our GMC-registered reviewing physician, summarising any out-of-range values, potential interactions between markers, and recommended next steps. If deficiencies are identified, the report will indicate whether self-supplementation is appropriate or whether a GP consultation is advisable. We recommend sharing the full report with your GP or endocrinologist, particularly if any thyroid markers are outside the reference range or if antibody levels are elevated, so that any treatment plan is informed by the complete picture.