Bone health, immune function, muscle signaling — and one of the most widespread nutrient deficiencies in the world, made worse by reduced eating.
Vitamin D3 (cholecalciferol) is the form of vitamin D produced by skin exposed to UVB radiation, and the form most efficiently converted to the active hormone calcitriol in the body. It is a fat-soluble vitamin that functions as a signaling molecule — vitamin D receptors are present in nearly every tissue type, including bone, muscle, immune cells, and the gut lining.
D3 is meaningfully more effective at raising and maintaining serum vitamin D levels than D2 (ergocalciferol), which is the form sometimes used in prescription supplements. For daily supplementation, D3 is the appropriate choice.
Vitamin D deficiency is estimated to affect 40–50% of the U.S. adult population — before any dietary restriction. The primary source for most people is sun exposure, not food, which means that diet alone rarely closes a deficiency gap. The few food sources of vitamin D (fatty fish, egg yolks, fortified milk) are also precisely the foods that get reduced when appetite drops on GLP-1 therapy.
Adequate vitamin D is required for calcium absorption and bone remodeling — particularly relevant when rapid weight loss can accelerate bone density loss. It also plays a role in muscle fiber composition and strength; deficiency is independently associated with reduced muscle power and increased fall risk. For people on GLP-1 therapy who are managing body composition, both of those functions matter.
2000 IU/day is a widely recommended supplemental dose for adults with typical deficiency risk — endorsed by major nutrition bodies as safe for long-term daily use and effective for maintaining serum 25(OH)D in the sufficiency range (≥30 ng/mL) for most adults. It avoids the toxicity risk of very high doses (typically above 10,000 IU/day for extended periods) while delivering meaningful repletion above the 600–800 IU RDA, which is set for minimum prevention rather than optimal function.
Vitamin D3 is part of Complete — Anchor's micronutrient formula for the vitamin gaps that reduced food intake creates. It works alongside Vitamin B12 to cover the two deficiencies most consistently observed in people on peptide therapy protocols.
Two ingredients. Two of the most common deficiencies on GLP-1 therapy. One daily stick.
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