Most people think of sleep as simply "rest." In reality, sleep is only one part of something much bigger.Every cell in your body runs on an internal biological clock known as your circadian rhythm. This 24-hour timing system coordinates almost every aspect of health, including:
- Sleep and wakefulness
- Energy production
- Hormone release
- Body temperature
- Digestion
- Immune function
- DNA repair
- Collagen production
- Cellular repair
- Inflammation
- Metabolism
- Cognitive performance
Scientists now recognise that maintaining a strong circadian rhythm is one of the foundations of healthy ageing. When this internal clock becomes disrupted, many biological systems begin to function less efficiently, contributing to accelerated biological ageing.
Your Body Doesn't Just Know What To Do...
It also knows when to do it.Different biological processes occur at different times of day. For example:
Morning
- Cortisol naturally rises
- Blood pressure increases
- Alertness improves
- Metabolism prepares for food
Daytime
- Digestion is most efficient
- Physical performance improves
- Learning and concentration peak
Evening
- Body temperature gradually falls
- Melatonin begins to rise
- Cells prepare for repair
- Digestion slows
Night
While you sleep your body carries out its "maintenance programme":
- DNA repair
- Cellular recycling (autophagy)
- Tissue repair
- Growth hormone release
- Immune regulation
- Memory consolidation
- Collagen production
- Brain waste clearance through the glymphatic system
This is why good sleep is not simply about feeling rested.It is when your body performs much of its repair and regeneration.
Every Cell Has Its Own Clock
Many people imagine the circadian rhythm exists only in the brain. In fact, every major organ has its own clock.
Including:
- Skin
- Liver
- Heart
- Gut
- Pancreas
- Immune cells
- Fat tissue
- Muscles
These clocks are coordinated by the brain's "master clock", the suprachiasmatic nucleus (SCN), which is synchronised primarily by light entering the eyes.
Circadian Rhythm and Biological Ageing
As we age, these biological clocks become less robust. The result can include:
- poorer sleep quality
- increased inflammation
- slower tissue repair
- insulin resistance
- reduced mitochondrial efficiency
- hormonal disruption
- weaker immune function
- reduced collagen production
Many researchers now believe circadian disruption is one of the contributors to accelerated biological ageing.
Circadian Rhythm and NAD+
One of the fascinating discoveries in longevity science is the close relationship between circadian rhythm and NAD+. NAD+ is essential for:
- mitochondrial energy production
- DNA repair
- activating sirtuins
- healthy ageing
NAD+ levels naturally fluctuate during the day.
The circadian clock helps regulate production of the enzyme NAMPT, which is central to recycling NAD+ through the salvage pathway. NAD+, in turn, activates sirtuin proteins that help regulate the body's biological clock. This creates a continuous feedback loop between circadian timing and cellular health.
Circadian Rhythm and Skin Health
Skin is one of the body's most active circadian organs. During daylight hours the skin focuses on protection. It:
- defends against UV exposure
- limits oxidative stress
- strengthens the skin barrier
At night the priorities change.
The skin increases:
- DNA repair
- collagen synthesis
- cell renewal
- barrier restoration
- recovery from environmental damage
Poor sleep or irregular circadian rhythms may reduce these repair processes and contribute to:
- premature ageing
- dull skin
- impaired barrier function
- delayed wound healing
- increased inflammation
- accelerated collagen loss
Six Ways to Optimise Your Circadian Rhythm
1. Wake at a Consistent Time
The single most important habit. Getting up at approximately the same time every day strengthens your internal clock more effectively than trying to "catch up" on sleep at weekends.
2. Get Morning Light
Natural daylight within the first hour after waking is one of the strongest signals for your brain. Aim for: 20–30 minutes outdoors. Even cloudy Irish mornings provide enough light to help synchronise your circadian clock.
3. Eat During a Consistent Time Window
Your digestive system also has a body clock. Eating at similar times each day supports healthy metabolism. Many researchers recommend avoiding constant grazing and allowing an overnight fasting period of around 12 hours. Time-restricted eating may help reinforce circadian rhythms in some people, although the ideal schedule varies by individual.
4. Exercise Most Days
Exercise helps regulate circadian timing. Consistency matters more than intensity. Many people perform best physically in the afternoon or early evening, when muscle function and body temperature are naturally higher.
5. Dim the Lights Before Bed
Artificial light—particularly blue light from phones, tablets and computers—suppresses melatonin production.
Try to:
- dim household lights
- reduce screen use
- use warm lighting
- create a calm bedtime routine
6. Avoid Late Evening Meals
Eating large meals close to bedtime means the digestive system is still working when the body is trying to repair itself. Allowing two to three hours between dinner and bedtime may improve sleep quality and reduce reflux in many people.
Lifestyle Habits That Disrupt Your Circadian Rhythm
Modern life often works against our biology.
Common disruptors include:
- irregular sleep schedules
- shift work
- jet lag
- excessive evening screen time
- late-night eating
- chronic stress
- insufficient daylight exposure
- too much artificial light after dark
Over time, repeated disruption can affect metabolism, immune function, cardiovascular health and healthy ageing.
Key Take-Home Message
Healthy ageing isn't only about what you eat or the skincare products you use.
It's also about when your body performs its essential repair work. By supporting your circadian rhythm through consistent sleep, morning daylight, regular meal timing, physical activity and a calming evening routine, you help optimise many of the body's natural repair systems—from mitochondrial function and DNA repair to collagen production and skin regeneration. For your clinic, this topic links naturally with your education on:
- Biological ageing
- The hallmarks of ageing
- Mitochondrial health
- NAD+ and sirtuins
- Inflamm-ageing
- Skin repair and collagen
- Sleep as an essential pillar of skin and whole-body health
The Duke Parameters are a set of formulation criteria established through the research of Dr. Sheldon Pinnell and colleagues at Duke University. Their work demonstrated that for pure L-ascorbic acid (vitamin C) to penetrate the skin effectively and provide meaningful antioxidant protection, it must meet three essential conditions.
The Duke Parameters
1. Pure L-Ascorbic Acid
- The vitamin C must be the pure, biologically active form: L-ascorbic acid.
- Derivatives such as magnesium ascorbyl phosphate, sodium ascorbyl phosphate or ascorbyl glucoside are generally more stable but must first be converted by the skin into L-ascorbic acid. This conversion can be limited, so they may not provide the same level of antioxidant activity as pure L-ascorbic acid.
2. Concentration Between 10% and 20%
- Below 10%, skin absorption and biological activity are significantly reduced.
- Around 15% provides excellent efficacy, which is why SkinCeuticals CE Ferulic and Silymarin CF contain 15% L-ascorbic acid.
- Increasing the concentration above 20% does not significantly increase absorption because the skin becomes saturated.
3. pH Below 3.5
- L-ascorbic acid must be formulated at a low pH (below 3.5) to remain in its non-ionised form.
- This allows it to penetrate the stratum corneum effectively.
- At higher pH levels, L-ascorbic acid becomes ionised and penetrates the skin much less efficiently.
Why Are the Duke Parameters So Important?
Dr. Pinnell's research showed that simply adding vitamin C to a skincare product does not guarantee it will work.
Unless a formulation meets these parameters:
- The vitamin C may not penetrate the skin.
- It may oxidise rapidly.
- It may provide little or no meaningful antioxidant protection.
- Clinical results are likely to be reduced.
These findings fundamentally changed how effective topical vitamin C products are formulated and remain the scientific foundation behind SkinCeuticals' antioxidant range.
SkinCeuticals and the Duke Parameters
SkinCeuticals was founded on this research and continues to formulate its L-ascorbic acid serums according to these principles:
|
Product |
L-Ascorbic Acid |
Meets Duke Parameters? |
|
CE Ferulic |
15% |
✓ |
|
Phloretin CF |
10% |
✓ |
|
Silymarin CF |
15% |
✓ |
|
Serum 10 AOX+ |
10% |
✓ |
Each is also formulated at a pH below 3.5 to maximise skin penetration.
The Take-Home Message
The Duke Parameters explain why not all vitamin C serums perform equally. A product may list vitamin C on the label, but unless it contains:
- Pure L-ascorbic acid,
- at a 10–20% concentration, and
- is formulated at a pH below 3.5,
it is unlikely to deliver the same level of proven antioxidant protection and collagen-stimulating benefits demonstrated in the original Duke University research. This scientific foundation is one of the main reasons SkinCeuticals' vitamin C serums continue to be regarded as the benchmark in topical antioxidant skincare.
Options re antioxidant Vitamin c Vitamin E Resveratrol CoQ10
There are many antioxidants used in skincare, but they differ significantly in how they work, their stability and the evidence supporting them. Each targets different types of oxidative stress, so combining antioxidants can provide broader protection than using one alone.
|
Antioxidant |
Primary Action |
Best For |
Evidence |
|
L-Ascorbic Acid (Vitamin C) |
Neutralises free radicals, stimulates collagen, brightens pigmentation |
Photoageing, wrinkles, pigmentation |
Excellent |
|
Vitamin E (Alpha-Tocopherol) |
Protects cell membranes and skin lipids from oxidation |
Dry, mature and environmentally damaged skin |
Excellent |
|
Resveratrol |
Potent polyphenol antioxidant that activates cellular defence pathways (including sirtuins in laboratory studies) |
Night-time repair, inflammation, ageing |
Good |
|
Coenzyme Q10 (Ubiquinone) |
Supports mitochondrial energy production while reducing oxidative stress |
Mature skin, fine lines, reduced cellular energy |
Good |
|
Ferulic Acid |
Stabilises vitamins C and E while providing additional antioxidant protection |
All skin types |
Excellent |
|
Phloretin |
Protects against pollution-related oxidative damage and helps improve pigmentation |
Oily skin, pigmentation |
Good |
|
Silymarin |
Reduces oxidation of sebum and helps protect against acne-related oxidative stress |
Oily and acne-prone skin |
Good |
|
Green Tea (EGCG) |
Anti-inflammatory and antioxidant |
Sensitive skin, redness |
Good |
|
Niacinamide (Vitamin B3) |
Reduces oxidative stress indirectly, improves barrier function and inflammation |
Almost all skin types |
Excellent |
|
Astaxanthin |
Extremely potent carotenoid antioxidant that protects lipids from oxidation |
Mature skin and UV protection |
Emerging but promising |
|
Glutathione |
Major intracellular antioxidant that helps recycle vitamins C and E |
Pigmentation and oxidative stress |
Moderate |
|
Idebenone |
Synthetic CoQ10 analogue with strong antioxidant activity |
Environmental ageing |
Moderate |
The Gold Standard Combination
One antioxidant rarely provides complete protection because different free radicals damage different parts of the cell.
The best-studied combination is:
- L-Ascorbic Acid (Vitamin C) – protects the water-based components of the cell and stimulates collagen.
- Vitamin E – protects lipid-rich cell membranes.
- Ferulic Acid – stabilises both vitamins and enhances their antioxidant activity.
This patented combination, developed by SkinCeuticals, has been shown to provide significantly greater protection against UV-induced oxidative damage than any of the ingredients alone.
Daytime Antioxidants
Morning is the ideal time for antioxidants because they help defend the skin against:
- UV radiation
- Pollution
- Infrared radiation
- Blue light
- Cigarette smoke
- Ozone
- Free radicals generated throughout the day
Antioxidants complement sunscreen—they do not replace it. Sunscreen helps prevent UV from entering the skin, while antioxidants neutralise free radicals that are generated despite sunscreen use.
Night-Time Antioxidants
At night, the skin shifts from protection to repair. Antioxidants that support cellular recovery include:
- Resveratrol – supports antioxidant defence and may influence longevity-related pathways in laboratory models.
- Coenzyme Q10 – supports mitochondrial energy production.
- Vitamin E – helps repair lipid membranes.
- Niacinamide – supports barrier repair and reduces inflammation.
Which Is the Most Effective?
If only one antioxidant is chosen, pure L-ascorbic acid (Vitamin C) has the strongest clinical evidence for improving skin health. It is unique because it not only neutralises free radicals but also stimulates collagen synthesis, helps reduce pigmentation and supports wound healing. However, from a scientific perspective, the greatest protection comes from combining complementary antioxidants, as each works in different cellular environments and targets different reactive oxygen species. This is why modern evidence-based formulations, such as SkinCeuticals CE Ferulic, combine multiple antioxidants rather than relying on a single ingredient.
Oxidation
Oxidation Explained
Oxidation is a natural chemical process that occurs continuously within the body. It happens when unstable molecules called free radicals react with healthy cells, stealing electrons from them. This damages important cellular structures, including DNA, proteins and fats (lipids).
Think of it like this:
- An apple turns brown when exposed to air – that's oxidation.
- Iron rusts – that's oxidation.
- Healthy skin cells can also undergo oxidation when exposed to UV light, pollution and other environmental stressors.
Our bodies naturally produce free radicals during normal metabolism, but external factors can dramatically increase their production.
What Causes Oxidation in the Skin?
The main sources include:
- UV radiation
- Pollution
- Cigarette smoke
- Blue light (to a lesser extent than UV)
- Infrared radiation
- Stress
- Poor diet
- Lack of sleep
- Alcohol
- Chronic inflammation
As free radicals accumulate, they create oxidative stress—a state where the body's antioxidant defences can no longer keep up.
What Happens During Oxidative Stress?
Oxidative stress damages:
- Collagen, leading to wrinkles and loss of firmness.
- Elastin, causing sagging and reduced elasticity.
- Cell membranes, weakening the skin barrier.
- DNA, increasing cellular dysfunction.
- Mitochondria, reducing energy production.
- Lipids (fats), leading to inflammation and barrier impairment.
Over time, this contributes to:
- Premature ageing
- Pigmentation
- Dull skin
- Slower healing
- Chronic inflammation
- Reduced skin resilience
How Antioxidants Help
Antioxidants protect the skin by donating an electron to free radicals without becoming unstable themselves. This neutralises the free radical before it can damage healthy cells.
Different antioxidants work in different parts of the cell:
- Vitamin C (L-ascorbic acid) protects the water-rich parts of cells and supports collagen production.
- Vitamin E protects the fatty cell membranes from oxidation.
- Ferulic acid helps stabilise vitamins C and E while adding further antioxidant protection.
- Resveratrol helps strengthen the skin's own antioxidant defence systems.
- Coenzyme Q10 (CoQ10) protects mitochondria, helping cells continue to produce energy efficiently.
Why This Matters in Skincare
Every day, your skin is exposed to oxidative stress. While sunscreen helps reduce UV exposure, it cannot neutralise all the free radicals generated by sunlight and pollution.
That's why dermatologists often recommend using an antioxidant serum—such as a well-formulated vitamin C—in the morning before sunscreen. Together, they provide complementary protection:
- Sunscreen reduces the amount of UV radiation reaching the skin.
- Antioxidants neutralise free radicals that are still produced.
The Key Message
Oxidation is a normal part of life, but excessive oxidation accelerates skin ageing. By combining daily sun protection with evidence-based antioxidants, maintaining a healthy diet rich in colourful fruits and vegetables, exercising regularly and getting adequate sleep, you help keep oxidative stress under control and support healthier, more resilient skin.
