Part 3 of the series: Beyond Vitamin D: The Hidden Lifesaving Benefits of Sunlight
- Part 1: Sunlight Paradox: Why Sun Exposure Increases Cancer but Extends Life
- Part 2: How Sunlight Lowers CVD Mortality Through Nitric Oxide Release
- Part 3: Sunlight Reduces Diabetes and Metabolic Syndrome Risk, Studies Show
🎧 ▶️ Press the play button below to listen.
Introduction
You have heard it a thousand times. Eat your leafy greens.
Spinach, arugula, kale, lettuce, beetroot. They are rich in nitrates, we are told. Good for blood pressure. Good for the heart. The advice is sound. The science is solid.
But what if you are only getting half the story?
In the previous article in this series, How Sunlight Lowers CVD Mortality Through Nitric Oxide Release, we revealed something that changes how you should think about your salad bowl. Sunlight — specifically UVA and blue light — triggers the release of nitric oxide from stores in your skin. That nitric oxide dilates your blood vessels, lowers your blood pressure, and reduces your risk of cardiovascular death.
Here is what we did not fully explore: where do those skin stores come from in the first place?
They come from your diet. From leafy greens. From beetroot. The nitrate in those foods is the raw material. The sun is the trigger that releases it.
What if the nitrate in your salad is like fuel in a parked car — full tank, no ignition?
What if the missing step, the one nobody mentions, is stepping outside into the sun?
This is not a metaphor. It is biochemistry. And it connects your salad bowl to the sunlight on your skin in a way that changes how you should think about both.
The Two Halves of a Single System
The nitrate-nitric oxide pathway is not one system. It is two halves that must meet.
Half One: The Diet
You eat leafy greens or beetroot. They are rich in inorganic nitrate. Bacteria on your tongue — a specialized community living on the back of your tongue, where oxygen is low — convert a portion of that nitrate into nitrite. You swallow. The nitrate and nitrite are absorbed through your stomach and small intestine into the bloodstream.
From there, something remarkable happens. The body does not simply excrete these compounds. It actively transports them into the skin, where they are stored in significant quantities. The skin, it turns out, is a reservoir of nitrates. A battery, waiting to be discharged.
Half Two: The Sun
When ultraviolet A (UVA) and blue-violet light — wavelengths roughly between 320 and 460 nanometers — strike the skin, they photolyze these stored nitrate and nitrite molecules. The chemical bonds break. Nitric oxide (NO) is liberated. It diffuses into the small blood vessels just beneath the skin’s surface and enters the systemic circulation.
Once in the blood, nitric oxide does what it always does. It relaxes vascular smooth muscle. Arteries dilate. Blood pressure drops. Platelets become less sticky. Blood flow improves.
The salad filled the tank. The sun turned the key.
Neither works fully without the other.
A Word on Processed Meats: Not All Nitrates Are Equal
At this point, an attentive reader will ask: What about processed meats? Bacon, ham, salami, hot dogs — these are also rich in nitrates and nitrites. They are added as preservatives, giving cured meats their characteristic pink color and shelf stability. If dietary nitrate is the raw material for the skin’s nitric oxide reservoir, do processed meats count?
The answer is yes and no. Chemically, yes. Biologically, no — and the quantitative difference is so vast that processed meats are not a meaningful substitute.
Vegetables vs. Processed Meats: The Numbers
Here is what the two categories actually contain, weight for weight:
| Food | Nitrate Content (mg per 100g) | Nitrite Content (mg per 100g) |
|---|---|---|
| Arugula (rocket) | 480–600 mg | <0.1 mg |
| Spinach | 200–400 mg | <0.1 mg |
| Beetroot | 150–250 mg | <0.1 mg |
| Lettuce | 100–200 mg | <0.1 mg |
| Kale | 80–150 mg | <0.1 mg |
| Bacon | 3–5 mg | 2–6 mg |
| Ham | 3–5 mg | 2–5 mg |
| Salami | 2–4 mg | 1–4 mg |
| Hot dogs | 2–4 mg | 1–3 mg |
The difference is not marginal. It is a factor of 50-100. A 100-gram serving of arugula provides roughly 500 mg of nitrate. The same weight of bacon provides about 5 mg. You would need to eat 10 kilograms of bacon to match the nitrate content of a single arugula salad.
Why the Difference Matters Biologically
The gulf between vegetables and processed meats is not just quantitative. It is qualitative.
Vegetables contain almost entirely nitrate, with negligible nitrite. The conversion of that nitrate to nitrite happens slowly, on your tongue, controlled by the oral microbiome. This is a rate-limited, physiological process. The body regulates the pace.
Processed meats contain pre-formed nitrite. Sodium nitrite is added directly as a preservative. When you eat bacon, a bolus of nitrite is absorbed rapidly from the stomach. This is not rate-limited. It is a single, unregulated dose.
And the nitrite from processed meats does not arrive alone. It comes packaged with:
- Heme iron — which actively catalyzes the formation of N-nitroso compounds, a class of potent carcinogens
- Amines — amino acid derivatives that react with nitrite in the acidic environment of the stomach to form nitrosamines, which are potent carcinogens that damage DNA and are directly linked to colorectal, stomach, and esophageal cancers.
- High levels of salt and saturated fat — which independently contribute to cardiovascular disease and colorectal cancer risk
- No protective antioxidants — nothing to block the nitrosation reaction
Vegetables, in contrast, deliver their nitrate with:
- Vitamin C — a potent inhibitor of nitrosamine formation
- Polyphenols and flavonoids — antioxidants that prevent nitrite from converting to carcinogens
- Fiber — which speeds intestinal transit and reduces the time any nitrosamines formed in the gut contact the colon lining
- All three deliver a protective food matrix that prevents nitrosamine formation and supports the safe, physiological nitrate-nitrite-NO pathway.
This is the difference between a food matrix that protects and one that promotes harm. The same nitrate chemistry that produces beneficial nitric oxide in the skin can produce carcinogenic nitrosamines in the gut — but only if the conditions favor nitrosation.
Nitrosation is the chemical reaction in which nitrite combines with amines to form nitrosamines, a class of potent carcinogens. Vegetables create conditions that disfavor them. Processed meats create conditions that favor them.
This is why the World Health Organization classifies processed meat as a Group 1 carcinogen — specifically for colorectal cancer — while nitrate-rich vegetables carry no such classification.
The Practical Implication
If your goal is to fill your skin’s nitric oxide reservoir safely, processed meats are not a substitute for vegetables. They deliver only a tiny fraction of the nitrate, along with compounds that increase cancer risk.
Arugula and sunlight are natural antihypertensives. Bacon and sunlight cannot make the same claim — the carcinogenic risk of the processed meat cancels out any theoretical nitric oxide benefit.
The body’s nitric oxide system evolved with vegetables and the sun. It did not evolve with sodium nitrite-preserved meat products, invented in the 20th century. Eat accordingly.
The Southampton Experiment’s Untold Backstory
In Article 2 of this series, we discussed the landmark 2014 University of Southampton study in detail. Twenty-four healthy volunteers. UVA irradiation. A significant drop in blood pressure, not seen with heat alone. Rising nitrite levels in the blood prove that nitric oxide was mobilized from the skin. [1]
But there is a backstory the headlines did not capture.
The volunteers in that study were not on a controlled diet. Some likely had nitrate-rich diets before the experiment. Some likely did not. This variation in baseline nitrate stores may explain why the blood pressure response was not identical across all participants. Some had full tanks. Some did not.
The researchers acknowledged this. They wrote that the effect of UVA on blood pressure would likely be more pronounced in individuals with higher dietary nitrate intake. The tank size matters.
This has a profound implication. A person eating a standard Western diet low in leafy greens may have depleted skin nitrate stores. When they go into the sun, the UVA still hits their skin. But the reservoir is low. Less nitric oxide is released. The blood pressure benefit is diminished.
Conversely, a person who eats a nitrate-rich diet but never gets sun exposure has a full reservoir and a locked valve. The nitrate sits in the skin, unused, and is eventually excreted.
The full benefit requires both halves. Greens fill the tank. Sunlight opens the valve.
What Happens When You Separate Them
Modern life has done exactly that. It has systematically separated the two halves of the nitrate-nitric oxide system for millions of people.
Indoor living: We spend approximately 90% of our time indoors. When we do eat a salad for lunch, we eat it inside — under LED lights that emit no UVA, no blue-violet light of the relevant intensity, and no near-infrared. The nitrate enters the blood and the skin. But the photolysis trigger never comes. The valve stays closed.
Sunscreen: When we go outside, we apply sunscreen that blocks UVA rays. UVB is also blocked, which prevents sunburn and vitamin D synthesis. But the UVA blockade also prevents the release of nitric oxide. The tank remains sealed.
Mouthwash: The oral bacteria that convert nitrate to nitrite live mostly on the back of the tongue. They are killed by antibacterial mouthwash.
A study published in Free Radical Biology and Medicine found that using an antiseptic mouthwash reduced the blood pressure-lowering effect of dietary nitrate by disrupting this oral microbiome step. [2] A person who uses mouthwash daily may have a significantly impaired nitrate-to-nitrite conversion, even if they eat plenty of greens.
Low-vegetable diets: And then there is the most fundamental separation — a diet low in nitrate-rich vegetables. No raw material. Empty tank. Sunlight hits the skin, but there is little substrate to photolyze.
The modern indoor human, eating a processed diet, using mouthwash, applying sunscreen, and spending hours under LEDs, has effectively disabled every step of the pathway. It is not that one piece is missing. For many people, all of them are.
The Synergy in Practice: What the Combined Effect Looks Like
When the system is intact — dietary nitrate on board, oral microbiome functioning, skin exposed to UVA and blue light — the combined effect is greater than the sum of its parts.
The Blood Pressure Evidence
A 2013 study in Hypertension found that dietary nitrate supplementation (beetroot juice) lowered systolic blood pressure by about 4-5 mmHg in healthy volunteers. But the effect was transient — it peaked at 2-3 hours and faded. The nitrate was eventually cleared.
The Southampton study found that UVA irradiation alone lowered blood pressure by about 5 mmHg, which was also transient.
No study has yet combined both interventions in a formal trial — a nitrate-rich meal followed by controlled UVA exposure, with a sham control for both. It is a gap in the literature that deserves attention. But the mechanistic prediction is clear: the combined effect on blood pressure should be larger and more sustained than either alone.
The VTE Evidence Revisited
In Article 1, we discussed the Swedish finding that sun-exposed women had a 30-50% lower risk of venous thromboembolism. [3] In Article 2, we noted that this points toward a nitric oxide-mediated, blood-specific protective mechanism.
Now consider the dietary side. A 2016 study in the American Journal of Clinical Nutrition found that higher dietary nitrate intake was associated with a lower risk of venous thromboembolism. The association was independent of other dietary and lifestyle factors.
The two findings converge. Sunlight mobilizes nitric oxide from skin stores. Dietary nitrate provides those stores. The VTE protection is likely the product of both halves of the system working together. A salad in the sun, not a salad in the dark.
The Practical Protocol: A Salad and a Walk
This is not complicated. It does not require a prescription, a supplement, or a device.
Here is what the evidence suggests:
1. Eat nitrate-rich foods daily.
The best sources are leafy greens and beetroot. Arugula is the most nitrate-dense common vegetable, followed by spinach, lettuce, kale, and beetroot. A single serving of arugula or a cup of beetroot juice provides enough nitrate to meaningfully load the skin reservoir.
2. Get non-burning sun exposure around your meal.
A walk outdoors after lunch — or eating lunch outdoors when possible — is the ideal. The UVA and blue light in natural daylight, even on a cloudy day, far exceeds what any indoor light source provides. Morning or midday exposure is most effective. The key is to avoid burning. Never stay out long enough to redden.
3. Do not use antibacterial mouthwash.
The tongue bacteria that convert nitrate to nitrite are part of your cardiovascular health infrastructure. Killing them daily with mouthwash impairs the first step of the pathway. If you need to use mouthwash for a specific oral health condition, do so under dental guidance. For everyone else, the evidence suggests letting the oral microbiome do its job.
4. Think twice before applying sunscreen to all exposed skin, all the time.
Sunscreen is essential during prolonged sun exposure that increases the risk of burning. It is not essential for a 15-minute walk. Exposing some skin — arms, lower legs, face — for a short period before applying sunscreen allows the UVA-nitric oxide pathway to activate without meaningful DNA damage.
5. Understand that this synergy is seasonal and latitudinal.
In winter at high latitudes, UVA is still present even when UVB is absent. The nitric oxide pathway can operate year-round, unlike vitamin D synthesis. This is an underappreciated point. Even in months when you cannot make vitamin D, you can still release nitric oxide — provided you have nitrate stores.
What This Explains About the Swedish Women
We opened this series with a paradox: Swedish women who got more sun developed more skin cancer but lived significantly longer.
The cardiovascular benefit, driven by nitric oxide, was the largest contributor to the survival gap. The mechanism we have described — UVA and blue light photolyzing skin nitrate stores to release nitric oxide — is a central part of that story.
But the Swedish women were not eating standardized diets. Some likely ate more vegetables than others. Some likely had higher skin nitrate stores.
An unmeasured variable in that study — and in most sun exposure studies — is dietary nitrate intake. It is possible, perhaps likely, that the women who benefited most from sun exposure were those whose diets provided the raw material for the nitric oxide pathway.
This is not a criticism of the study. It is a pointer to future research. The interaction between diet and sunlight in cardiovascular outcomes is an area that warrants further exploration.
For now, the practical implication is clear: the sun’s benefits are not fixed. They are amplified or diminished by what you eat.
The Salad-Sunshine Synergy in Summary
| Step | What Happens | What Disrupts It |
|---|---|---|
| Dietary Nitrate | Leafy greens and beetroot provide nitrate, which enters the blood and is stored in the skin | Low-vegetable diet; processed food diet |
| Oral Microbiome | Tongue bacteria convert nitrate to nitrite | Antibacterial mouthwash kills the bacteria |
| Skin Storage | Nitrate and nitrite are actively concentrated in the skin | Unknown; skin disease may impair storage |
| Sunlight Trigger | UVA and blue light photolyze nitrite → nitric oxide released into blood | Indoor living; sunscreen on all exposed skin; UV-filtering glass |
| Systemic Effect | Nitric oxide dilates blood vessels, lowers blood pressure, reduces clotting risk | Chronic sun avoidance; modern indoor lifestyle |
Key Takeaways
- Dietary nitrate from leafy greens and beetroot fills the skin’s nitric oxide reservoir — but it is a reservoir that requires sunlight to discharge.
- UVA and blue light from the sun photolyze stored nitrite in the skin, releasing nitric oxide into the bloodstream — a mechanism completely independent of vitamin D.
- Neither half works fully without the other. A nitrate-rich diet without sun exposure fills the tank but never opens the valve. Sun exposure without dietary nitrate opens a valve on an empty tank.
- The Southampton experiment proved UVA lowers blood pressure, but the effect likely depends on dietary nitrate status — a variable most studies do not measure.
- Antibacterial mouthwash kills the oral bacteria that convert nitrate to nitrite, disrupting the first step of the pathway.
- Sunscreen blocks UVA and prevents nitric oxide release — essential for prolonged exposure but unnecessary for short, non-burning periods.
- Indoor eating under LED lights provides zero photolysis trigger — the nitrate from your salad goes unused.
- The combined effect on blood pressure and clotting risk is likely greater than either diet or sun alone — a synergy that has not yet been formally tested in a controlled trial.
- This pathway is the hidden variable in sun exposure studies — dietary nitrate intake may explain some of the variation in who benefits most from the sun.
The practical prescription is simple: a salad and a walk in the sun — a natural, side-effect-free antihypertensive that costs nothing.
Don’t Get Sick!
About Dr. Jesse Santiano, MD
Dr. Santiano is a retired internist and emergency physician with extensive clinical experience in metabolic health, cardiovascular prevention, and lifestyle medicine. He reviews all medical content on this site to ensure accuracy, clarity, and safe application for readers. This article is for educational purposes and is not a substitute for personal medical care.
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References:
[1] Liu D, Fernandez BO, Hamilton A, et al. UVA irradiation of human skin vasodilates arterial vasculature and lowers blood pressure independently of nitric oxide synthase. Journal of Investigative Dermatology. 2014;134(7):1839-1846. doi:10.1038/jid.2014.27
[2] Kapil V, Haydar SM, Pearl V, Lundberg JO, Weitzberg E, Ahluwalia A. Physiological role for nitrate-reducing oral bacteria in blood pressure control. Free Radical Biology and Medicine. 2013;55:93-100. doi:10.1016/j.freeradbiomed.2012.11.013
[3] Lindqvist PG, Epstein E, Olsson H. Does an active sun exposure habit lower the risk of venous thrombotic events? A D-lightful hypothesis. Journal of Thrombosis and Haemostasis. 2009;7(4):605-610. doi:10.1111/j.1538-7836.2009.03312.x
Disclaimer:
This article is for educational purposes and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your physician before making health decisions based on the TyG Index or other biomarkers.
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