HeyJaredSarah Kleiner
This Substack is where I teach you how your body works through the lens of light, circadian biology, nutrition and mitochondrial health. Practical tools you can use every single day, how small daily shifts create huge changes, and how to build health!
- Indexed issues, last 90 days
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- Sep 29, 2026
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- Jul 15, 2026
Latest issues
Your Vitamin D Winter Kit (opens the original)
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At the end of summer every year I get the same question: “Okay, so what should my levels actually be?”Fair question. The internet will tell you 30, 50, 80, or “as high as possible,” depending on who you ask (and at the end of the article I will tell you WHERE those numbers even come from).So today I’m giving you the full breakdown: what’s realistic, why so many people are low right now even after a summer outside, and the kit I’d want everyone to have going into the darker months. If you don’t k
Why you get so sad when your tan fades (opens the original)
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TLDR: I’ve seen a lot of posts online about being “sad to lose the tan”….and the thing most people don’t realize is that there is real science here. Sunlight runs an entire feel-good cascade in your skin, eyes, and brain all summer, and it’s slowing down with lower angle sun and less UV, but you aren’t screwed! Your body was built to handle winter. (And I usually still have tan lines in January.)Today I’m going to drop the science on this as well as my Vitamin D map (with an explanation of how I
Brand New Iron Deficiency Guidelines just dropped & I have thoughts (opens the original)
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The new iron deficiency guidelines just dropped, and I have thoughtsBack in June of this year - my hemoglobin was normal. My iron panel was “normal”. My doctor looked at me and said there was nothing to treat…..even though I was cold all the time - exhausted all the time, had restless legs & my ferritin was a NINE.My labs had also been trending the in wrong direction for six months straight, and by the old rulebook, that didn’t count as anything. Not anemic - so we tell you it’s probably “someth
Sharing some of my NOT so good labs with you (opens the original)
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Hey - Thanks for hanging with me in all of this low ferritin content if you joined my Substack to learn about sunlight and health.I have a lot of great articles planned for fall and winter (it was 87 degrees here today so that’s why I haven’t been in a rush to produce all of that!).On Friday I was thrilled to learn my ferritin tripled and my entire iron panel improved. I also learned that my metabolic and immune markers had all improved across the board (read more on all that HERE).You can also
I tripled my ferritin in 90 days (opens the original)
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As promised - I am sharing my most recent labs after being “on a mission” since June to fix my entire iron panel (as well as improve my T3 - and Neutrophil to Lymphocyte ratio).I will share more details regarding everything I have done so far in another article in the future (diet changes - stress - habits - minerals - gut health & more) ……as well as my plan going forward…..so make sure you are subscribed if you want to read that when it is ready.Substack is w
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