Vitamin D - The Sunshine Vitamin

This article is written by Izzy who just completed a degree in Nutrition, Exercise and Health at Plymouth University and is registered with the Association for Nutrition. Izzy is currently undergoing a MSc in Applied Sports Nutrition at St. Mary’s (remotely) alongside working at an independent running specialist shop on Dartmoor. Also, a level 3 personal trainer and a firm advocate of the importance of strength training. Outside of the gym, Izzy enjoys swimming and skiing; although loves anything involving adventuring in the outdoors. She strongly believes that a balanced diet should be at the foundation of any athlete’s nutrition and that this should be established through a healthy relationship with food and good habits. Izzy also believes that nutrition should hold a stronger importance in the national curriculum seeing as it impacts every single one of us every day.

Vitamin D - The Sunshine Vitamin

It is widely known that consuming a colourful diet, rich in diversity and flavour, is the best

way in which to meet our micronutrient needs and function at our optimum. However, as the days get shorter and the trees start to change colour around this time every year, there is one nutrient in particular that becomes difficult to obtain from our external environment.

Vitamin D can be synthesised by our skin when exposed to sunlight. But during the winter

months in the UK, the levels of ultraviolet B radiation in sunlight are no longer sufficient for

this process to take place, so it is a good idea to get it elsewhere [1] .

Vitamin D can be found in some foods. Oily fish (such as salmon or mackerel) is a good

source, but this is not eaten regularly by most people, let alone daily. Egg yolks are another,

but one egg contains only approximately 5% of your daily vitamin D requirement. Some

breakfast cereals may also be fortified in small amounts. How about some liver? Anyone?

It is very difficult to achieve a sufficient intake through food alone [2] . This is why Public

Health England and the NHS recommend that everyone from the age of 1 takes a 10μg or

400IU supplement daily between the months of October and April in the UK [3, 4] .

So why is vitamin D important?

- Increased risk of upper respiratory tract infection

- Increased risk of fracture due to impaired calcium absorption

- Inferior muscle repair

- Impaired strength & power performance

During developmental years, bone density should be gradually increasing. At age 30-35, we reach our individual peak bone mass, a figure largely determined by nutrition and activity levels during childhood and adolescence [5] . From this age onwards, bone density very gradually decreases; a process that can be slowed through exercise and diet [6]. Our bones and teeth hold 99% of the body’s calcium. Calcium has important uses within the body, such as being a key player in muscle contraction and nerve impulses. If the body has insufficient calcium to carry out bodily functions, it will take from this reservoir we store in our bones. If this is a common occurrence, it can be detrimental to bone strength. Therefore, adequate calcium intake is necessary to maintain as much bone density as possible as we age [7] .

Vitamin D regulates calcium uptake by maximising the number of transporters and receptors in the gut lining, enabling the absorption of calcium from digested food into the blood stream [8] . So adequate vitamin D is necessary to ensure we can uptake enough calcium (obviously dependant on adequate calcium in the diet).

Vitamin D is also known to play a significant role in immune function, important for maintaining a strong defence against the horrible bugs and illnesses associated with winter months [9, 10] .

Consequences of insufficient vitamin D

In extreme scenarios, deficiencies in vitamin D can result in rickets and osteomalacia in

children and adults respectively [11] . Both diseases are characterised by soft, weak bones and have scarily seen an increase in prevalence in recent years; potentially because more young people lead sedentary lifestyles and spend increasing amounts of time indoors – the critical years during which much of their bone mass is accrued [1] .

For active adults who spend time in the summer sunshine, vitamin D deficiency throughout

the winter and thus reduced calcium absorption may be more likely to display itself later on

in life in the form of osteoporosis (yes, this does require some of you to think far into the

future – something we should all base our daily actions on if we want to maintain strength,

mobility and independence into old age).

Osteoporosis affects over 3 million people in the UK and significantly increases fracture risk

and subsequent reduced quality years of life [12] . This can be as a result of gradual and

consistent depletion of calcium stores from our bones over the years through insufficient

vitamin D and/or calcium intake. It could also be because of a lack of physical activity. Of

course, the older we live, the longer we need our bones to support us for too!

Women are at a higher risk of suffering from osteoporosis due to rapid bone loss in the

years following menopause, so maintaining as much bone density as possible is

advantageous in reducing likelihood of disease later in ladies! [13]

What about athletes?

As runners and athletes, the activity side of things to maintain strong bones is hopefully in

the bag; particularly if we are doing strength work to support our running. But the importance of maintaining bone strength aided by a healthy diet may be escalated due to higher impact and stress we are subjecting our bodies to [14] . Running increases load through the body and magnifies the pressure our bones are under. Combine that with the prevalence of RED-S or relative energy deficiency in sport, and we have a problem. Stress fractures are becoming all too common in the running world – likely through a combination of under- fuelling and over-training. Female athletes in particular need to be aware of their micronutrient intake as they typically consume a lower-energy diet so getting everything they need from their food can be more challenging [15, 16] .

More exercise also equates to increased muscle contraction, a mechanism dependant on

calcium intake. So, it may be even more important for athletes to supplement vitamin D

than sedentary individuals [17] . Vitamin D deficiency prevalence in athletes is thought to be

over 50% overall and has been found even higher during winter and spring [14] .

Regarding performance, multiple studies have found that vitamin D supplementation in

deficient athletes improved exercises such as sprinting and jumping and also reduced injury

rate [18, 19] . This could be useful in interval training to improve running speed, for example,

achieving more adaptations from training with adequate vitamin D levels in the body.

Some final points

Supplements containing vitamin D3 are best absorbed and it does not matter which brand

you buy as long as it provides at least the recommended 10μg/day. It may be worth

checking if this is already included if you take a multivitamin.

If you are in doubt whether it is safe to take a supplement or are on any medication, please

seek further advice from your GP or a dietician. It is also possible to get a blood test with

some doctors if you are interested or concerned about your micronutrient levels.

The older generation or at-risk populations (such as post-menopausal women) may benefit

from a higher dose so, again, please seek further medical advice if interested or concerned.

A combination of adequate vitamin D, calcium and weight-bearing activity is essential for

optimum bone health. Taking a vitamin D supplement through the winter months is one

way to ensure we are satisfying this triad of important considerations, for our today selves

and also our future selves.


1. Spiro, A., & Buttriss, J. (2014). Vitamin D: An overview of vitamin D status and intake in Europe. Nutrition Bulletin, 39(4), 322-350.

2. Calvo, M., Whiting, S., & Barton, C. (2005). Vitamin D Intake: A Global Perspective of Current Status. The Journal Of Nutrition, 135(2), 310-316.

3. SACN (2016) Vitamin D and Health. Retrieved 17 November 2020, from

4. NHS (2020). Vitamins and minerals - Vitamin D. Retrieved 17 November 2020, from

5. Saggese, G., Baroncelli, G., & Bertelloni, S. (2002). Puberty and bone development. Best Practice & Research Clinical Endocrinology & Metabolism, 16(1), 53-64.

6. Weaver, C., Gordon, C., Janz, K., Kalkwarf, H., Lappe, J., & Lewis, R. et al. (2016). Erratum to: The National Osteoporosis Foundation’s position statement on peak bone mass development and lifestyle factors: a systematic review and implementation recommendations. Osteoporosis International, 27(4), 1387-1387.

7. Cashman, K. (2002). Calcium intake, calcium bioavailability and bone health. British Journal Of Nutrition, 87(S2), S169-S177.

8. Fleet, J., & Schoch, R. (2010). Molecular mechanisms for regulation of intestinal calcium absorption by vitamin D and other factors. Critical Reviews In Clinical Laboratory Sciences, 47(4), 181-195.

9. Etten, E., & Mathieu, C. (2005). Immunoregulation by 1,25-dihydroxyvitamin D3: Basic concepts. The Journal Of Steroid Biochemistry And Molecular Biology, 97(1-2), 93-101.

10. White, J. (2008). Vitamin D Signaling, Infectious Diseases, and Regulation of Innate Immunity. Infection And Immunity, 76(9), 3837-3843.

11. Thatcher, T., & Clarke, B. (2011) Vitamin D insufficiency. Mayo Clinic Proceedings, 86, 50-60

12. NHS (2019) Osteoporosis. Retrieved 17 November 2020, from

13. Macdonald, H., Mavroeidi, A., Barr, R., Black, A., Fraser, W., & Reid, D. (2008). Vitamin D status in postmenopausal women living at higher latitudes in the UK in relation to bone health, overweight, sunlight exposure and dietary vitamin D. Bone, 42(5), 996-1003.

14. Goolsby, M., & Boniquit, N. (2016). Bone Health in Athletes. Sports Health: A Multidisciplinary Approach, 9(2),108-117.

15. Barrack, M., Gibbs, J., De Souza, M., Williams, N., Nichols, J., Rauh, M., & Nattiv, A. (2014). Higher Incidence of Bone Stress Injuries With Increasing Female Athlete Triad–Related Risk Factors. The American Journal Of Sports Medicine, 42(4), 949-958.

16. Wentz, L., Liu, P., Haymes, E., & Ilich, J. (2011). Females Have a Greater Incidence of Stress Fractures Than Males in Both Military and Athletic Populations: A Systemic Review. Military Medicine, 176(4), 420-430.

17. Tenforde, A., Sayres, L., Sainani, K., & Fredericson, M. (2010). Evaluating the Relationship of Calcium and Vitamin D in the Prevention of Stress Fracture Injuries in the Young Athlete: A Review of the Literature. PM&R, 2(10), 945-949.

18. Knechtle, B., & Nikolaidis, P. (2020). Vitamin D and Sport Performance. Nutrients, 12(3), 841.

19. Hamilton, B. (2010). Vitamin D and Human Skeletal Muscle. Scandinavian Journal Of Medicine & Science In Sports, 20(2), 182-190.

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