Dr Tim Pearce
A randomised controlled trial with over 3,000 participants found that ending a shower with 30 seconds of cold water reduced self-reported sickness absence from work by 29% compared to controls. That’s the kind of specific, evidence-based finding that changes a vague wellness conversation into something useful, and it’s exactly the type of research you can share with patients who mention fatigue, low energy, or feeling run down during aesthetic consultations.
This article covers two areas of emerging research relevant to whole-patient conversations: targeted micronutrient adequacy (specifically the vitamin D and K relationship, including weight-adjusted dosing) and controlled cold exposure. Both offer practitioners credible material for discussing resilience and wellbeing with patients who raise these topics.
Hormesis describes a biological response where brief, moderate stressors trigger adaptive changes that enhance cellular function and stress tolerance, and Calabrese and Mattson (2017) describe this as a “coordinated response” allowing an organism to improve performance and resilience by managing limited biological resources more effectively. The concept underpins both areas of research covered here and provides useful context for understanding why controlled stress exposure, whether through cold water or other means, can produce beneficial adaptive responses.
The role of Vitamin D in calcium absorption is well established, but its synergy with Vitamin K is often overlooked in clinical practice, and according to Aaseth et al. (2024), these two fat-soluble vitamins function as cooperative agents in maintaining bone health and regulating calcium metabolism through a precise mechanism. Vitamin D facilitates calcium absorption from the intestines into the bloodstream, while Vitamin K is required for the post-translational carboxylation of Vitamin K-dependent proteins (VKDPs), most notably osteocalcin, which once activated by Vitamin K has the unique ability to import calcium from blood directly into the bone matrix, incorporating it into hydroxyapatite for increased mineralisation. Aaseth et al. (2024) emphasise that adequate Vitamin K alongside optimal Vitamin D status is essential for reducing osteoporosis risk and ensuring calcium does not settle in vascular tissues, which provides a useful framework for discussing why Vitamin D alone may be insufficient when patients ask about bone health or calcium supplementation.
Standard supplementation guidance often fails patients with higher BMIs, and the research explains why this happens at a physiological level. Ekwaru et al. (2014) analysed over 22,000 observations and found that Body Mass Index is a primary determinant of serum 25-hydroxyvitamin D (25(OH)D) levels because Vitamin D, being fat-soluble, becomes sequestered in body fat compartments and significantly reduces its bioavailability in the bloodstream, which has substantial practical implications for how clinicians should approach dosing.
The findings suggest that obese participants may require two to three times more Vitamin D supplementation than individuals of normal weight to achieve equivalent serum targets, and Holick (2025) notes that while 3,500 IU daily might be reasonable for a normal-weight adult to reach healthy levels, this would be inadequate for an obese patient. Clinicians should therefore consider weight-specific dosing to ensure at-risk patients achieve circulating 25(OH)D concentrations of at least 40-50 ng/mL, which is the level sufficient to reduce risks for chronic conditions including Type 2 Diabetes and autoimmune disorders according to the research. This information is directly relevant to aesthetic practice, where patients frequently discuss weight alongside appearance concerns and may never have received weight-adjusted guidance from other healthcare providers.
Returning to the cold-shower research mentioned at the outset, the Buijze et al. (2016) “Cool Challenge” trial assigned over 3,000 participants to end their daily warm shower with 30, 60, or 90 seconds of the coldest available water, and the 29% reduction in sickness absence was observed across all cold-shower groups compared to controls. Participants did not report fewer days of illness, but the intensity of their symptoms appeared to be modulated, making them more capable of functioning despite mild infections, and Cain et al. (2025) note in their systematic review that routine cold-water immersion delivers longer-term benefits for immunity and general quality of life.
The threshold for benefit was notably low at just 30 seconds, which makes this an accessible conversation for patients who express interest in non-pharmacological approaches to building resilience and improving their energy levels.
Beyond immune function, cold water produces measurable effects on mood that have been documented in controlled research settings. Kelly and Bird (2022) examined the effects of a single cold-water immersion on young, healthy individuals and found a significant decrease in negative affect with a large effect size, with the immersion group reporting reductions in tension, anger, depression, fatigue, and confusion alongside significant increases in vigour and esteem-related affect.
These effects likely stem from the cold-shock response, which triggers activation of the sympathetic-adrenal-medullary and hypothalamic-pituitary-adrenal (HPA) axes, and the resulting release of cortisol and beta-endorphins is associated with improved emotional stability and hardiness according to the researchers. For patients mentioning low mood or fatigue alongside their aesthetic concerns, this research offers a simple, cost-free intervention they can explore, though any discussion of cold exposure should include appropriate cautions about using slow and controlled entry into cold water to mitigate the risks of cold shock, particularly for those with underlying cardiovascular conditions.
These are conversations you can have in two minutes during a consultation. The research is peer-reviewed, published in journals including Nutrients, PLoS ONE, and Lifestyle Medicine, and the advice is low-risk. For patients who’ve never heard weight-adjusted vitamin D guidance or the cold-shower data, it may be genuinely useful information that changes how they think about their own resilience and wellbeing.
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This article is for general information only. It does not provide medical advice or recommend any treatment.
Aaseth, J.O., Finnes, T.E., Askim, M., & Alexander, J. (2024). The Importance of Vitamin K and the Combination of Vitamins K and D for Calcium Metabolism and Bone Health: A Review. Nutrients, 16, 2420.
Buijze, G.A., Sierevelt, I.N., van der Heijden, B.C.J.M., Dijkgraaf, M.G., & Frings-Dresen, M.H.W. (2016). The Effect of Cold Showering on Health and Work: A Randomized Controlled Trial. PLoS ONE, 11(9), e0161749.
Cain, T., Brinsley, J., Bennett, H., Nelson, M., Maher, C., & Singh, B. (2025). Effects of cold-water immersion on health and wellbeing: A systematic review and meta-analysis. PLoS ONE, 20(1), e0317615.
Calabrese, E.J., & Mattson, M.P. (2017). How does hormesis impact biology, toxicology, and medicine? npj Aging and Mechanisms of Disease, 3, 13.
Ekwaru, J.P., Zwicker, J.D., Holick, M.F., Giovannucci, E., & Veugelers, P.J. (2014). The Importance of Body Weight for the Dose Response Relationship of Oral Vitamin D Supplementation and Serum 25-Hydroxyvitamin D in Healthy Volunteers. PLoS ONE, 9(11), e111265.
Holick, M.F. (2025). The Debatable Clinical Utility of the 2024 Vitamin D Guideline: Bridging the Gap Between Current Guidelines, Practical Clinical Recommendations, and Utilization of Emerging Evidence in Vitamin D Disease Prevention. Endocrine Practice, 31, 399-402.
Kelly, J.S., & Bird, E. (2022). Improved mood following a single immersion in cold water. Lifestyle Medicine, 3, e53.
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