Vitamin D: Andrew Huberman & Dr. Rhonda Patrick
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Far from being a simple vitamin, vitamin D is a potent steroid hormone produced in our skin upon exposure to sunlight.
This understanding reframes its importance and sheds light on why widespread deficiency poses a significant public health concern.
Sunlight, Skin, and Vitamin D Deficiency
The body's ability to synthesize vitamin D is a complex process, influenced by factors like skin melanin content, sunscreen use, and age.
Dr. Rhonda Patrick highlighted a pivotal University of Chicago study demonstrating this variability: individuals with darker skin, which offers natural sun protection, required approximately six times longer sun exposure to produce the same amount of vitamin D as those with fair skin.
This natural adaptation becomes a modern-day challenge. People with darker skin residing in less sunny regions (like Minnesota, where UVB radiation is limited to about four months a year) struggle to maintain adequate levels. Compounding this, our increasingly indoor lifestyles affect everyone. "Seventy percent of the US population has inadequate vitamin D levels," Patrick noted, defining this as less than 30 nanograms per milliliter (ng/mL) by Endocrine Society standards. For optimal health and reduced all-cause mortality, meta-analyses suggest levels between 40 to 60 ng/mL.
Huberman added a crucial perspective, emphasizing that the term "vitamin D" obscures its hormonal nature. He pointed out that our skin is not merely a protective barrier but an endocrine organ capable of producing hormones. He cited a recent Israeli study showing regular sun exposure significantly increased testosterone and estrogen levels via a specific biological pathway, further underscoring the skin's active endocrine role.
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Vitamin D's Impact on Genes and Serotonin
The true power of vitamin D lies in its vast regulatory functions.
Patrick explained that as a steroid hormone, it binds to receptors that ultimately control gene expression. The vitamin D receptor complex enters the cell nucleus, recognizes specific DNA sequences known as vitamin D response elements (VDREs), and subsequently activates or deactivates a multitude of genes.
Startlingly, Patrick revealed that vitamin D regulates "more than 5% of the protein-encoded human genome"—a figure that has grown since her in-depth research between 2012 and 2014. One of her fascinating discoveries from that period, published in 2014, identified VDREs in the genes coding for tryptophan hydroxylase. This enzyme is critical for converting the amino acid tryptophan (obtained from food) into serotonin.
The process differs between the gut and the brain. Since serotonin cannot cross the blood-brain barrier, tryptophan must enter the brain to be converted by tryptophan hydroxylase II—an enzyme Patrick's research found is activated by vitamin D. Conversely, her work suggested that the gut version (tryptophan hydroxylase I) might be repressed by vitamin D, hypotheses later confirmed by other researchers.
Beyond serotonin, vitamin D's influence extends to immune system function, blood pressure regulation, water retention, and bone homeostasis. Its reach is so extensive, Patrick asserted, that it's difficult to overstate its importance.
Given this, Huberman remarked, "I'm beginning to think that this [widespread deficiency] could be the linchpin in a number of really important issues," potentially underlying various population-wide health problems.
Vitamin D Supplementation and Testing
For many, supplementation with vitamin D3 is a practical approach. However, individual needs vary significantly. Huberman shared that while he takes 5,000-10,000 IU of vitamin D3 daily, a healthy family member required 30,000 IU to reach normal levels, highlighting the necessity of personalized strategies.
Patrick clarified that vitamin D3 is generally the preferred form for supplementation, whereas vitamin D2 often comes from plant sources or fortified foods (like milk and non-dairy alternatives). However, dietary sources alone are rarely sufficient to correct a deficiency. Age is a key factor, as older individuals convert vitamin D less efficiently. Genetic variations (SNPs) also play a significant role, with Patrick noting, "There's a variety of SNPs that basically make that conversion inefficient."
"Measuring your vitamin D levels before and after supplementation is the only way you're gonna figure that out," Patrick stressed. "You can't know what you don't measure." This is crucial because Mendelian randomization studies link genetic variants affecting vitamin D conversion to higher all-cause mortality, respiratory-related mortality, cancer-related mortality, and increased risk for conditions like multiple sclerosis.
For those without such genetic complications, Patrick offered a useful guideline: 1,000 IU of vitamin D typically raises blood levels by about 5 ng/mL. Thus, to go from 20 to 40 ng/mL, one might need around 4,000 IU.
Timing of supplementation (relative to sun, food, or time of day) is not considered critical due to vitamin D's slow-acting hormonal nature.
For those hesitant to test, Huberman admitted he once supplemented with 5,000 IU daily without prior testing. Patrick reassured that vitamin D toxicity (hypercalcemia) is "extremely hard to get," typically requiring "hundreds of thousands of IU a day for a long time." She personally takes 5,000 IU daily, maintaining her levels around 50 ng/mL, combined with some sun exposure (protecting her face but allowing exposure on other body parts).
Beyond supplements, the amount of skin exposed to sunlight is paramount for natural production. Huberman emphasized, "The amount of skin that you expose is important... Laying out on your back deck in shorts and a T-shirt with arms exposed and legs exposed is a very different stimulus than walking around in jeans and a sweatshirt." While covered exposure might still benefit circadian rhythms via light to the eyes, it does little for vitamin D synthesis, a point Patrick strongly affirmed.
Is Sunscreen Safe?
The discussion then turned to sun protection, where Huberman voiced significant concerns about chemical sunscreens, stating he's "as scared of sunscreen as I am of melanoma."
His apprehension centers on ingredients that can cross the blood-brain barrier. "There's a reason why there's a blood brain barrier, a blood ovary and a blood testes barrier," he explained, highlighting the vulnerability of non-regenerating neurons and areas with genetic material.
Patrick shared she typically opts for mineral sunscreens (which are reflective) over chemical ones. She further elaborated on concerns that some chemical sunscreen ingredients, while protecting from UV radiation, may react with sunlight to form reactive oxygen species and potentially carcinogenic compounds—an ironic twist. "I know that some of them react with the sun and while they do protect from the UVA and or B, they like form massive reactive oxygen species and carcinogen," Patrick stated, acknowledging this area requires more definitive research.
Huberman proposed a "journal club" to scrutinize scientific papers on sunscreen ingredients, given their widespread use and the public's limited awareness of potential transdermal absorption and risks.
As a simple, effective alternative, Patrick suggested: "Wear a hat." This practical advice, coupled with sensible sun exposure for vitamin D production, offers a balanced approach.
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Wrapping Up
Understanding vitamin D as a crucial hormone, recognizing the prevalence of deficiency, and being mindful of how we achieve and maintain optimal levels—through strategic sun exposure, informed supplementation, and careful consideration of sun protection methods—are vital for overall health and well-being.