Vitamin D and Sunlight: What the Evidence Actually Says

The guideline is more conservative than the marketing

Vitamin D is sold as something nearly everyone should be testing and supplementing -- immunity, mood, bone health, general vitality. The actual clinical guidance is narrower. In 2024, the Endocrine Society published an updated clinical practice guideline on vitamin D for the prevention of disease, and it explicitly does not recommend routine screening or supplementation for the general healthy adult population. A separate systematic review of a decade of evidence-based guidelines found the same pattern across the board: two-thirds of guidelines recommend screening only for people already at elevated risk, and none recommend population-wide screening or supplementation for healthy adults with no risk factors.

Where the Endocrine Society's panel does suggest empiric (untested) vitamin D supplementation is for specific groups: children and teens aged 1-18, adults over 75, people who are pregnant, and people with high-risk prediabetes. For those groups, and for others found to be low on testing, most guidelines recommend supplementation in the range of 400 to 1,000 IU per day, targeting a blood level of roughly 50-75 nmol/L -- not the much higher doses sometimes marketed as an immune or energy booster.

• The Endocrine Society's 2024 guideline does not recommend routine vitamin D screening or supplementation for the general healthy adult population.
• A systematic review of the last decade of guidelines found the same conservative pattern: screening is recommended only for specific at-risk groups, never the general population.
• Groups where empiric supplementation IS suggested: ages 1-18, adults over 75, pregnancy, and high-risk prediabetes -- typically 400-1,000 IU/day, not high-dose regimens.

Sunlight is the body's main source -- but dermatology and endocrinology don't fully agree on it

More than 90% of the body's vitamin D is made in the skin from UVB exposure, not from diet or supplements. That single fact creates a genuine, unresolved tension between two fields of medicine. The American Academy of Dermatology's position is direct: healthy adults should get vitamin D from diet and fortified foods or supplements, not from sun exposure or tanning beds, because there is no level of UV exposure that maximizes vitamin D synthesis without also increasing skin cancer risk.

Other researchers push back on treating that as the final word. Some published reviews argue that regular, moderate, non-burning sun exposure ('sensible sun exposure') is associated with lower skin cancer risk than the pattern that actually drives most skin damage: infrequent, intense, burning exposure. The distinction these researchers draw is between brief, controlled exposure of the torso and limbs (with the face protected) versus unprotected exposure long enough to burn. This is a genuine, unresolved disagreement between camps of medical researchers -- not a settled question -- so we're presenting both positions rather than picking one for you.

• Over 90% of the body's vitamin D is normally produced by UVB exposure to skin, not diet or pills.
• The American Academy of Dermatology's position: get vitamin D from diet/supplements, not sun exposure, because no UV dose is both cancer-safe and vitamin-D-optimal.
• Other researchers argue brief, non-burning sun exposure is associated with lower skin cancer risk than the burn-prone pattern that actually damages skin -- a genuine open disagreement, not settled.

What this actually means for you

If you're a healthy adult with no risk factors, the current guidelines do not tell you to run out and get a vitamin D blood test or start supplementing -- that's the part the wellness-marketing version of this topic tends to skip. If you fall into one of the higher-risk groups above, have symptoms that could reflect a deficiency (bone pain, unusual fatigue, muscle weakness), or have a condition that affects vitamin D absorption or metabolism, that's a conversation for your physician, including whether a blood test is actually warranted and what level and duration of supplementation makes sense for you specifically. We are not going to tell you a number to take -- that decision, and the dose, belongs to you and your doctor.

The safety gate: this is not a self-diagnose-and-dose situation

Vitamin D is fat-soluble, which means -- unlike water-soluble vitamins -- your body stores excess rather than simply excreting it, and very high, sustained doses can build up to the point of toxicity, causing elevated blood calcium with symptoms like nausea, weakness, and in serious cases kidney problems. People with kidney disease, sarcoidosis, hyperparathyroidism, or a history of kidney stones should not start vitamin D supplementation without medical supervision. Pregnant people, and anyone on medications that interact with vitamin D metabolism, should also loop in their physician before starting or changing a supplement regimen. None of this is a reason to avoid vitamin D entirely -- it's a reason to let a blood test and a physician set the number instead of a supplement label.

A quick honest recap

• The Endocrine Society's 2024 guideline does not recommend routine vitamin D screening or supplementation for the general healthy adult population -- only for specific higher-risk groups.
• A decade of pooled guidelines confirms the same conservative pattern: no guideline recommends population-wide screening.
• Over 90% of vitamin D is normally made via sun exposure to skin, but dermatology and some vitamin D researchers genuinely disagree on how to weigh that against skin cancer risk.
• Vitamin D is fat-soluble and can reach toxic levels with sustained high dosing -- this is a blood-test-and-physician decision, not a self-dose-based-on-a-label decision.