The importance of Vitamin D
by Sarah Ann Macklin, ANtur.
WHY WE NEED TO TAKE NOTICE OF VITAMIN D
As we begin 2021, we may be feeling a little low with the dark and cold weather we are submitted to in the UK. With a lack of sunshine available this does affect our health in copious ways, because we cannot gain any vitamin D. Even on the sunniest of days in the winter, the ultraviolet B (UBV) rays are still not strong enough to penetrate our skin.
IS IT VITAMIN D A VITAMIN OR HORMONE?
Vitamin D is technically not a vitamin, it is actually a steroid hormone. Our bodies can manufacture it. It is derived from cholesterol and circulates in our blood, binding to receptors which play a host too many biological actions such calcium and phosphate metabolism, our immune system and building strong healthy bones.
WHERE CAN WE GAIN IT?
Our main source of vitamin D comes from UVB sun exposure and is produced endogenously in the skin, which is our main source of vitamin D known as cholecalciferol (D3) . Vitamin D can also be obtained from the diet, but in much more limited amounts, known as ergocalceiferol (D2). Foods which include vitamin D are oily fish such as salmon and mackerel, liver, egg yolks, mushrooms grown under UV light and some fortified foods such as dairy products and cereals.
Around 90% of vitamin D is gained through sun exposure, but our ability to make vitamin D is influenced by external factors, such as time of day, season, latitude, cloud cover, air pollution, shift work, clothing and sunscreen can all affect the efficiency of vitamin D levels obtained (1).
For example, those living in the northern hemispheres such as the UK, may not be gaining sufficient vitamin D through UVB radiation between October to March and therefore, will be at risk of deficiency. In these months it is recommended by Public Health England (PHE) to supplement with 10 micrograms (ug). However, in 2020 due to the SARS-COV2 outbreak and limited time spent outdoors, it is now recommend to supplement throughout the year with 10 ug.
HOW IS IT MEASURED?
Serum concentrations of 25-hydroxvitamin D 25 (OH)D is the main indicator of vitamin D status. 25 (OH) D levels under <20ng/ml and vitamin D insufficiency as 21-29ng/mg (2). If worried about your vitamin D levels, it is important to ask your GP for a blood test to check them.
WHO ELSE IS AT RISK?
Approximately 1 in 5 people in the UK have low vitamin D levels. Low vitamin D levels are associated with a higher risk of poor musculoskeletal health, poor muscle strength, low moods and immunity.
There are certain groups who risk deficiency more than others. Infants who are breastfed may be at risk of vitamin D deficiency, and are recommended to be given a supplement of 8.5 – 10 ug/day, due to breast milk containing low levels of vitamin D. (3). Breastfeeding mothers should also take a vitamin D supplement of 10ug/day. Babies fed infant formula should not be given a vitamin D supplement if there infant formula is forfeited with vitamin D and drinking up to+ 500mls/day. Children aged 1-4 years should be given a daily supplement containing 10ug/day.
Nearly 50% of Asians and a third of black Africans living in the UK are severely deficient in vitamin D (4) Efficiency is decreased with darker skin pigmentation (5), increasing age (6) and intestinal malabsorption disorders (7) and therefore, these groups should will be at risk of increased deficiency.
If you are exposed to very little sunshine, which is very fitting with 2020 (due to the amount of time spent in doors this year), cover your skin for cultural reasons or work mainly night shifts it is recommend to supplement with 10ug/day throughout the year. People who are aged 65 years and older or are from a minority ethnic group for example, African, African-Caribbean, black or south Asian origin may also be at risk and are recommend 10ug/day.
People who are on very restrictive diets such as low fat or vegan may also be at risk of a vitamin D deficiency. Individuals who suffer with fat absorption such as liver disease, cystic fibrosis, celiac disease, Crohn’s or ulcerative colitis may also be at risk, as vitamin D is fat soluble it depends on the guts ability to absorb dietary fat.
WHY IS VITAMIN D SO IMPORTANT?
Vitamin D has always been spoken about primarily with calcium and phosphate metabolism which helps keep our musculoskeletal health healthy and strong. Vitamin D enhances absorption of calcium in the small intestine and is therefore essential for calcium absorption. Vitamin D also helps promote mineralization of the collagen matrix in bone. If we have low vitamin D levels, calcium is conserved and this can cause many problems throughout your life cycle. If a child has very low vitamin D status they are at risk of developing rickets, where bone deformities, bone pain, weak bones and slow growth occur. In adolescents this can cause osteomalacia and osteopenia in adults. In the ageing populations, low vitamin D status put individuals at risk of fractures and osteoporosis.
However, in more recent years vitamin D has been associated with many other areas of health. Vitamin D receptors are found in every cell in the body, and its therefore no surprise that vitamin D can play a part in many areas with our health. 2020 has brought vitamin D into the spotlight with immunity. Vitamin D has been linked with modest protective effects to help with respiratory tract infections (8), but it does not prevent or treat SARS-COV2. There has been a growing body of literature which has found associations between depression and vitamin D status (9). Vitamin D has also been linked to a rise in inflammation as well helping aid weight loss.
References
1. SACN (2016) https://www.gov.uk/government/publications/sacn-vitamin-d-and-health-report
2. Holick, M., Binkley, N., Bischoff-Ferrari, H., Gordon, C., Hanley, D., Heaney, R., Murad, M. and Weaver, C., 2011. Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline. The Journal of Clinical Endocrinology & Metabolism, 96(7), pp.1911-1930.
3. Goldacre, M., Hall, N. and Yeates, D., 2014. Hospitalisation for children with rickets in England: a historical perspective. The Lancet, 383(9917), pp.597-598.
4. Watkins, J., 2020. Preventing a covid-19 pandemic. BMJ, p.m810.
5. Clemens, T., Henderson, S., Adams, J. and Holick, M., 1982. INCREASED SKIN PIGMENT REDUCES THE CAPACITY OF SKIN TO SYNTHESISE VITAMIN D3. The Lancet, 319(8263), pp.74-76.
6. MacLaughlin, J., Holick, M. and Kasper, K., 1986. Aging Decreases the Capacity of Human Skin to Produce Vitamin D3. Nutrition in Clinical Practice, 1(1), pp.57-58.
7. Jurado, G. and Kazlauskaite, R., 2006. Abstract #257: Shall AACE Initiate a Practice Guideline for Screening, Diagnosis, and Treatment of Vitamin D Deficiency in Adults?. Endocrine Practice, 12, p.40.
8. Jolliffe, D., Greenberg, L., Hooper, R., Griffiths, C., Camargo, C., Kerley, C., Jensen, M., Mauger, D., Stelmach, I., Urashima, M. and Martineau, A., 2017. Vitamin D supplementation to prevent asthma exacerbations: a systematic review and meta-analysis of individual participant data. The Lancet Respiratory Medicine, 5(11), pp.881-890.