The clocks have gone back, the evenings are drawing in, and many of us are spending less time outdoors. As winter approaches, we're often reminded to think about our vitamin D intake. But while its role in maintaining healthy bones and muscles is well established, research is uncovering a more complicated relationship between vitamin D, our physical health and psychological wellbeing.
Vitamin D has been studied in relation to depression, sleep disturbances, neurodevelopmental conditions and other aspects of health. Not all these relationships are fully understood, and an association does not necessarily mean that one factor causes another. Nevertheless, the findings raise important questions about how different aspects of our health interact, and what may happen when physical and psychological difficulties begin to compound one another.
For World Vitamin D Day, we explore some of the research findings that deserve closer attention.
Could vitamin D be part of the relationship between sleep and mental health?
Sleep is fundamental to emotional regulation, concentration, memory and psychological wellbeing. When sleep becomes disrupted, the consequences can extend well beyond tiredness, affecting our ability to manage stress, maintain relationships and participate in everyday activities.
Interestingly, researchers have found associations between vitamin D levels and sleep quality.
A systematic review and meta-analysis of 19 intervention studies found that vitamin D supplementation was associated with improvements in sleep quality in some studies, although findings concerning sleep duration and specific sleep disorders were less consistent.
This raises an interesting question about how physical and psychological difficulties might interact.
Consider someone experiencing poor sleep alongside low mood. They may feel increasingly fatigued, struggle to concentrate and withdraw from activities they previously enjoyed. Reduced activity and disrupted routines may then make it more difficult to establish consistent sleep patterns, potentially perpetuating the difficulties.
If vitamin D deficiency is also present, it may be another relevant factor to investigate, although research has not established that deficiency causes this cycle.
What does this mean?
When someone experiences persistent tiredness, low mood or sleep difficulties, it is important to consider the wider picture. Sleep patterns, emotional health, physical symptoms and possible nutritional deficiencies may all warrant attention, rather than assuming there is a single explanation.
Why might neurodivergent children be more vulnerable to nutritional deficiencies?
For some autistic children, eating is shaped by sensory experiences that can make particular textures, smells, tastes or temperatures difficult to tolerate. This can result in a restricted range of accepted foods, even when children and families are making considerable efforts to maintain a balanced diet.
A 2025 systematic review and meta-analysis, examining 32 studies involving 18,480 children, found that autistic children had lower average intakes of several nutrients, including vitamin D, compared with non-autistic children. Lower vitamin D levels were also identified.
The implications extend beyond nutrition alone.
Imagine a child whose sensory sensitivities restrict their diet. Mealtimes may become stressful, concerns about nutritional adequacy may increase parental anxiety, and attempts to introduce unfamiliar foods may create further distress. If clinically significant nutritional deficiencies develop, associated physical symptoms could add another difficulty to the child's everyday functioning.
A physical health concern may therefore become intertwined with sensory needs, family relationships and emotional wellbeing, with each requiring its own consideration.
This research does not suggest that vitamin D deficiency causes autism or that supplementation treats autistic characteristics. Instead, it highlights the importance of recognising nutritional vulnerabilities that may accompany sensory differences.
What does this mean?
When supporting neurodivergent children, nutritional health should be considered alongside sensory experiences, emotional needs and family circumstances. Persistent dietary restriction may benefit from assessment by an appropriately qualified healthcare professional, with support that respects the child's sensory needs rather than increasing pressure around food.
Could depression itself increase the risk of vitamin D deficiency?
One of the most interesting questions in vitamin D research concerns the direction of the relationship between vitamin D and depression.
Numerous observational studies have identified associations between low vitamin D levels and depressive symptoms. A 2024 meta-analysis of 31 clinical trials also found that supplementation was associated with reductions in depressive symptoms, particularly in shorter-term studies.
However, this does not mean that vitamin D deficiency necessarily causes depression. Nor does it establish supplementation as an effective treatment for everyone experiencing depressive symptoms.
There is another possibility worth considering: depression may itself influence the behaviours that affect vitamin D levels.
Someone experiencing depression may have less motivation to leave the house, prepare meals, exercise or maintain established routines. Reduced time outdoors can affect vitamin D production during the months when sunlight is sufficient, while dietary changes may reduce intake.
This creates the possibility of a reciprocal relationship, where psychological difficulties increase vulnerability to certain physical health problems, which may then add to the person's overall burden of symptoms.
Research from the UK Biobank cohort has explored these overlapping relationships, recognising that outdoor activity, vitamin D status and depressive symptoms may influence one another or share other underlying causes.
What does this mean?
The relationship between mental and physical health works in both directions. When someone experiences persistent depression, consideration of nutrition, physical activity and general medical health can complement psychological assessment and treatment, rather than replacing them.
Could physical discomfort be contributing to changes in mood or behaviour?
Vitamin D deficiency is most clearly associated with its effects on bones and muscles. Severe or prolonged deficiency can lead to osteomalacia in adults, causing bone pain and muscle weakness, while deficiency during childhood can contribute to rickets.
These physical consequences can have wider implications for everyday functioning.
Consider an older adult who experiences increasing muscle weakness or discomfort. Physical activities may become harder, independence may decrease, and opportunities for social contact may gradually diminish. Over time, reduced participation and isolation may contribute to poorer psychological wellbeing.
For children, physical discomfort may sometimes present less clearly. A child experiencing pain or weakness might become reluctant to participate in activities, appear more irritable or struggle with demands that previously felt manageable.
None of these changes is specific to vitamin D deficiency. There are many possible medical, developmental and psychological explanations. However, they illustrate why behavioural or emotional changes should not automatically be understood in isolation from physical health.
The NHS guidance on vitamin D explains the established consequences of deficiency for musculoskeletal health.
What does this mean?
Changes in mood, behaviour or participation can sometimes reflect physical difficulties that have not yet been recognised. Where there are persistent symptoms, understanding what has changed physically as well as emotionally can be an important part of assessment.
What happens when shorter days affect more than our vitamin D levels?
The clocks changing brings attention to the seasonal reduction in daylight, but the effects of light on our health extend beyond vitamin D production.
Exposure to natural daylight helps regulate circadian rhythms, the biological processes that influence sleep, alertness and daily patterns of activity.
A large UK Biobank study involving more than 400,000 participants found that greater time spent in outdoor daylight was associated with better sleep-related outcomes and lower levels of reported low mood and depressive symptoms.
Importantly, these findings concern daylight exposure, not vitamin D supplementation. The benefits of natural light for circadian regulation should not be confused with vitamin D production.
Nevertheless, the findings reveal how seasonal changes may affect several aspects of health simultaneously.
For someone already experiencing disrupted sleep, low mood or reduced physical activity, shorter days may make existing routines harder to maintain. Less time outdoors can mean fewer opportunities for exercise, social interaction and daylight exposure, potentially compounding psychological difficulties.
During the same season, reduced UVB exposure also limits the body's ability to produce vitamin D.
These are distinct processes, but they can occur alongside one another.
What does this mean?
Looking after wellbeing during winter involves more than vitamin supplementation. Maintaining opportunities for daylight exposure, regular movement, social connection and consistent sleep routines may all be important, particularly for people who already experience difficulties with mood or daily functioning.
Why a whole-person approach matters
Taken together, these findings illustrate something important about our health: physical symptoms, nutritional status, emotional experiences and everyday circumstances rarely exist independently.
A child experiencing sensory-related dietary restrictions may face nutritional vulnerabilities alongside difficulties around mealtimes. An adult experiencing depression may gradually withdraw from activities that support physical health. Someone living with persistent discomfort may experience changes in sleep, independence and emotional wellbeing.
In each situation, focusing exclusively on the most visible symptom risks overlooking other factors that may be contributing to the person's difficulties.
Vitamin D is one example of why a broader understanding of health matters. It is not a universal explanation for fatigue, depression, neurodevelopmental differences or sleep problems, and the research does not support treating it as such. But ensuring adequate vitamin D intake is an established part of maintaining physical health, while identifying genuine deficiencies can be an important aspect of appropriate medical care.
At The Integratis Clinic, the relationship between physical and psychological health is reflected in the breadth of services available. Alongside psychological therapies for children, young people and adults, Functional Medicine offers an opportunity to explore nutritional, physiological and lifestyle factors that may contribute to health concerns.
Understanding an individual's needs means considering how different aspects of their health and circumstances interact, rather than viewing each difficulty in isolation.
What should we be doing about vitamin D this winter?
In the UK, sunlight between October and early March is not sufficient for most people to produce adequate vitamin D.
The NHS recommends that adults and children over four consider taking a daily supplement containing 10 micrograms (400 IU) during autumn and winter. Children aged one to four should receive a daily supplement throughout the year, while specific guidance also applies to babies and people at increased risk of deficiency.
Routine vitamin D blood testing is not necessary for everyone. However, where there are concerning symptoms or particular risk factors, a healthcare professional can advise whether testing or further assessment is appropriate. High-dose supplementation should not be undertaken without appropriate medical guidance.
Read the NHS guidance on vitamin D.
If you would like to explore how physical health, nutrition and lifestyle factors may be contributing to your wellbeing, find out more about Functional Medicine at The Integratis Clinic, or contact the clinic to arrange an initial conversation.
