I keep mine above 65
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The highest possible level through sun exposure is 60 ng/ml.
Source:
Low Vitamin D Status despite Abundant Sun Exposure
https://academic.oup.com/jcem/article-abstract/92/6/2130/2597445
Apparently, there are a number of variables, with some populations exceeding 100 through sun exposure.
Highest Vitamin D Levels
• Indigenous populations in Tanzania, such as the Maasai and Hadzabe, have some of the highest recorded mean serum 25(OH)D levels, with studies reporting averages over 106 nmol/L, and pregnant Maasai women averaging up to 138.5 nmol/L.
• Vietnam has mean levels around 92 nmol/L for men and 75 nmol/L for women, which are also among the highest globally outside of Africa.
• Populations in the Gambia also show higher-than-global-average vitamin D levels, with mean values around 91 nmol/L in women aged 45–80.
Key Factors Influencing High Levels
• Sunlight exposure is the main reason, as these populations often live near the equator with abundant year-round sun and engage in outdoor lifestyles.
• Minimal clothing restrictions allow for more skin exposure to ultraviolet B, promoting natural vitamin D synthesis.
• Diets with some fish and non-industrialized habits may also support higher vitamin D status in some Asian populations, like Japan and Vietnam