Vitamin D – Could You Be Running Low?

Vitamin D is a fat soluble nutrient meaning we need dietary fat to absorb it, and we store excess in our body fat for later use.  Interestingly, vitamin D is not a true vitamin as it can be made in the body.

When our skin is exposed to UV light, usually from the sun, provitamins react and are converted to vitamin D metabolites, mainly in the liver and kidneys.  Cholesterol is important for this process.  Unfortunately, our indoor lifestyles and weak-winter sun in the northern hemisphere reduce our chances for sun exposure, therefore increasing our risk of vitamin D deficiency.  We are also cautious about sun exposure and the risk of damage to our skin – a very real risk which needs to be balanced.

Individuals with darker skin types are likely to be less efficient at making vitamin D and are therefore at increased risk of deficiency.

Bones and heart

Vitamin D is best associated with bone health because it helps to regulate calcium levels and absorption from the bloodstream into bones.  In doing this, it also protects the heart as high levels of calcium in the blood can reduce the heart muscles’ ability to relax and increased blood pressure (hypertension).  This is why some people with hypertension may be given calcium-channel blockers.

Vitamin D also helps to balance cholesterol levels.  It is associated with increased HDL (‘good’) cholesterol and reduced LDL (‘bad’) cholesterol, therefore supporting cardiovascular health.

Muscle strength

Some studies involving people over the age of 50 years old, have found that vitamin D has beneficial effects on leg muscles strength and physical performance.  Studies have also found that vitamin D supports the repair of injured muscles.  More research is required to confirm the findings and determine the mechanism.

Immunity and asthma

Vitamin D has been found to play a role in the immune system.  Studies have linked it to lower risks of infections, inflammation, and autoimmune conditions such as MS, type 1 diabetes and rheumatoid arthritis.

Low vitamin D has also been associated with asthma flare-ups and less effective management of asthma.

Mood and cognition

Low vitamin D has been associated with an increased risk of developing several neurological disorders including depression, autism, Alzheimer’s disease, epilepsy and schizophrenia.  However, the cause and mechanisms involved are unclear, it is thought that vitamin D has a role in the development of neurons, the production of neurotransmitters (chemical messengers in the brain) and the production of serotonin (the ‘happy hormone’).  Vitamin D supplementation is not currently considered to be a cure for these conditions.

Blood sugar management

Low vitamin D has been associated with poorer blood sugar management.  It is thought to affect insulin production, release and action.  It may also increase the risks of systemic inflammation.

Exposing the skin on your face and arms (at least, as appropriate) to outdoor sunlight each day between April and October, ideally for up to 20 minutes, is the best way to support your vitamin D levels naturally.  To do this however, it is worth noting that suncream blocks the UV light from being absorbed by the skin and therefore reduces its effectiveness.  It cannot be denied however that suncream is important to help reduce the risk of skin damage.

To spend time in the sun without suncream while reducing the risk of sun exposure:

• Try to avoid the hottest part of the day – get outdoors early morning and in the cooler evenings in the summer to avoid the strongest sun. Staying in the shade will still expose you to UV light but at lower levels than direct sun – this will help protect your skin but could also reduce your vitamin D production.  Remember UV light does not penetrate glass so being in a conservatory or car will not help your vitamin D levels.
• Consider your skin type – if you burn easily you will need to reduce your exposure time. May be having several short burst of time in the sun would work better for you.  When you are out keep the boniest bits like your shoulders covered as they will burn first.  With pale skin and freckles I burn fairly easily and so I always wear a t-shirt instead of vest tops when I’m gardening to protect my shoulders.  I also keep a cardigan or hoody tied around my waste to help protect my lower back when I’m bending a lot – I’ve had a 2000s/2010s Doctor Who logo there a few times!
• Check medications. Some medications can affect your skin’s sensitivity to the sun putting you at greater risk of sunburn and skin damage than you would otherwise be.  Make sure you check the information leaflet and refer to a pharmacist if you have any concerns.
• Remember to protect your eyes from bright sunlight – bright light can damage the retina and lens of the eye.
• Make sure you keep adequately hydrated, especially on hot days. Being dehydrated can contribute to tiredness and even heat stroke.

Food Sources

Vitamin D is available in some foods, but not many and only in small amounts and should not be relied on to prevent deficiency.  Foods that provide some vitamin D include:

• Oily fish
• Mushrooms grown under UV light (they may be marked as containing vitamin D)
• Fortified cereals and milk replacements.

Testing

Routine NHS blood tests do not include vitamin D – despite all research findings suggesting associations between low vitamin D and ill-health symptoms.  If you are concerned about your levels you can your GP to run the test (they can also refuse!), or seek a private test.  As part of my nutritional therapy packages I can arrange test kits (at extra cost), ensuring results are interpreted in the context of your overall health.

It is possible to have too much vitamin D, however this is usually only a risk if you take high-dose, or unnecessary, supplements for a long time.  Too much vitamin D may contribute to:

• Hypervitaminosis D
• Hypercalcemia (too much calcium), which may progress to affecting the kidneys

Signs of too much vitamin D include decreased appetite, nausea, constipation, weakness, increased urination and bone pain.

• Latest Knowledge on the Role of Vitamin D in Hypertension – Jensen, et al (2023) – https://pmc.ncbi.nlm.nih.gov/articles/PMC10003079/
• Vitamin D Promotes Skeletal Muscle Regeneration and Mitochondrial Health – Latham, et al (2021) – https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2021.660498/full
• A Review of the Critical Role of Vitamin D Axis on the Immune System – Daryabor, Gholijani and Kahmini (2023) – https://www.sciencedirect.com/science/article/pii/S0014480023000175
• The Relationship Between Vitamin D and Asthma Exacerbation – Ogeyingbo, et al (2021) – https://pmc.ncbi.nlm.nih.gov/articles/PMC8389855/
• Effectiveness of Vitamin D on Neurological and Mental Disorders – AlGhamdi (2024) – https://pmc.ncbi.nlm.nih.gov/articles/PMC11202759/