Diet therapy

Vitamin D for growth and immunity

All vitamins are important for health but recent research around Vitamin D is highlighting just how important it is for growth and the maintenance of our immune system.

What is vitamin D?

Often called ‘The Sunshine Vitamin’, Vitamin D3 (cholecalciferol) is a fat-soluble vitamin which is found naturally in animal containing foods such as fish liver oil, tuna, salmon, eggs, beef and lambs fry. 1

It can also be added in the plant form vitamin D2 (ergocalciferol) to fortify foods such as margarine and fat spreads; some reduced-fat diary products, milk, dried milk as well as plant based dairy substitutes such as soy drinks, soy yoghurt and liquid meal replacements. 2

Our body can also make vitamin D3 from sunlight.  When the ultraviolet B, or UVB, rays in sunlight hit the skin, it activates 7-dehydrocholesterol to produce pre-vitamin D3 which is then carried in the blood stream to the liver. Here it is modified (hydroxylated)  into 25-hydroxy-vitamin D (25(OH)D) and then onto the kidneys where it is converted into the biologically active form 1,25(OH)2 vitamin D3.
Obviously vitamin D produced in this way is subject to considerable seasonal variation, with cloud cover and pollution all reducing UVB rays, particularly in winter.

How much do we need?

The minimum required intake of Vitamin D3/day 1

Children: Birth to 18 years 5 µg
Adults: 19-50 years 5 µg
51-70 years 10 µg
>70 years 15 µg


As vitamin D is made up of dietary as well as cutaneous production standards of sufficiency are set using serum 25(OH)D and nutritional adequacy determined as follows:

Deficiency      <25nmol/L
Insufficient     25-49.9nmol/L
Adequate        >50nmol/L

Note 1:

1 µg cholecalciferol is equal to 0.2 µg 25(OH)D.
Vitamin D is also sometimes expressed in International Units where 1 IU equals 0.025 µg cholecalciferol or 0.005 µg 25(OH)D.

Some researchers are now calling for levels of adequacy to be raised to 25(OH)D >75-100 nmol/L  particularly for high risk athletes and the elderly.1 Also better absorption appears to come when Vitamin D is administered in daily or weekly doses rather than one bolus /mega dose.3

A blood test can quickly determine Vitamin D status.  If considering supplementation be guided by your doctor regarding the amount and dosage as Vitamin D is a fat soluble vitamin that can be accumulated by the body and can be toxic if consumed in excessive amounts. (NB: Toxicity is less likely to come from sunlight than from an excess of supplementation).

What does Vitamin D do?

As Vitamin D3 can be formed in the skin, yet go on to affect other organs such as the bones, gut and kidneys, it can also be called a hormone and part of the endocrine system. Hormones signal to the body what to do and when to do it for example when to build up calcium in bone and when to break it down or remodel it. 2

Bones, joints and muscles

Vitamin D is essential for the absorption of calcium, magnesium and phosphorus which are important for bone growth, density, remodeling and strength and without adequate amounts, bone loss or injury will occur.

A lack of Vitamin D can cause Rickets a disease in young people that reduces the calcification (hardening) of the growing ends (epiphyses) of bones, causing bone weakness, bowed legs, deformity of joints and stooped posture.

Long bones can be particularly at risk of under mineralization during the pubertal growth spurt when young athletes are still trying to achieve peak bone density so a good vitamin D status during this period is important for growth and to prevent painful stress fractures. 2

There is limited evidence regarding vitamin D and improved muscle strength in adolescents, however poor vitamin D status (<20ng/mL) was found to reduce forearm muscle strength when a group of 301 Chinese female adolescent athletes were compared with individuals with adequate levels.4

It is thought that when individuals with low vitamin D status receive supplementation, muscle strength may be gained due to an  increase in the size and amount of type 2 (fast twitch) muscle fibres. 2

Essential body processes

On a daily basis 80% of vitamin D in the body is involved in the autocrine pathway responsible  for regulating electrolyte metabolism, gene expression; protein synthesis; cell turnover; immune and inflammatory responses 2 making this an essential vitamin to maintain body processes and growth.

Respiratory function and immunity

A higher prevalence of pneumonia and respiratory infection has been observed in children with rickets and low vitamin D status. 2, 3

Although there is no separate data on children or athletes a recent meta-analysis of 23 studies covering 11,901 participants with Covid-19 found most of these patients were suffering from vitamin D deficiency/insufficiency. 5

It was estimated that when vitamin D levels are low there is a 3.3% chance of getting infected with SARS-CoV-2  and the chance of developing Covid 19 was found to be 5 times higher in people with vitamin D deficiency 5

Groups at risk of vitamin D deficiency

Dark skinned people

Reaching an adequate intake of vitamin D can be problematic for people living at latitudes >35 degrees where UVB radiation is absent during winter, or for those who have naturally dark skin, such as people from Africa, India and the Middle East.6

Athletes who train indoors

Vitamin D deficiency can affect outdoor athletes who avoid the sun by training early in the day or evening or athletes who wear protective clothing (e.g ice hockey) or who spend long periods of time training indoors. 7

People on energy or nutrient restricted diets

Also at risk are athletes and people who might be following energy restricted or fad diets to maintain low body weights such as gymnasts, dancers and jockeys.7 People exclusively following vegan and vegetarian diets or those who are trying very low energy diets e.g. intermittent fasting, need to take particular care and have regular blood tests to check adequacy.

Excessive users of sunscreen

The excessive use of sunscreen can reduce Vitamin D absorption from the sun. However it is still important to prevent skin cancer so stay ‘sun smart’ if exercising outdoors – that is, wear a hat and use sunscreen in sensible amounts and if possible avoid training during the hottest times of the day.

The elderly or malnourished

Elderly people, particularly if hospitalized or in residential care; people (of all ages ) who are fussy eaters ;or recovering from surgery;  those with limited access to sunlight and food intake are definitely at risk of vitamin D deficiency.

Multiple studies of the elderly have linked low vitamin D to reduced reaction times, poor balance and an increased risk of falling. Also studies show vitamin D supplementation can bring improvements in strength, walking distance and a reduction in general discomfort. 1  Making vitamin D an essential nutrient in later life.

Vitamin D for better health

While there is limited research linking vitamin D supplementation with performance enhancement at the moment it is never the less very important for the prevention of chronic and acute disease such as cancer, cardiovascular disease, type 2 diabetes, autoimmune disease and infectious disease 2 so be sure to discuss Vitamin D with your doctor and sports dietitian if you have concerns.


  1. Nutrient Reference Values for Australia and New Zealand’16 January 2020,
  2. Organ, D; Pritchett, K. Vitamin D and the athlete: risks, recommendations and benefits. Nutrients 2013 June; 5 (6) 1856-1868.
  3. Martineau, A; Jollife, D.A; Hooper, R.C., Vitamin D supplementation ot precent acute respiratory tract infection: a systematic review, meta-analysis of individual participant data. BMJ 2017, 356.
  4. Foo L.H., Zhang Q., Zhu K., Ma G., Hu X., Greenfield H., Fraser D.R. Low vitamin D status has an adverse influence on bone mass, turnover, and muscle strength in adolescent female girls.J. Nutr. 2009;139:1002–1007.
  5. Ghasemian, R; Shamshirian, A; Heydari, K; Malekan, M; Alizedeh-Navaei, R; Ebrahimzadeh, M.A; Warkiani, M.E; Jafarpour, H; Bazaz, S.R; Shahmirzadi, A.R; Khodabandeh, M; Seyfari, B; Motamedzadeh, A; Dadgostar, E; Aalinezhad,M; Sdaghat, M; Razzaghi, N; Zarandi, B; Asadi, A; Naei, V.Y; Beheshti, R; Hessami, A; Azizi, S; Mohseni, A.R; Shamshirian, D. The role of vitamin D in the age of Covid-19: A systematic review and meta-analysis. The Intern. J. of Clini. Prac. 29 July 2021
  6. Desbrow, B., Burke, L.M., Cox, G., Fallon, K., Hislop, M., Logan, R., Marino, N., Sawyer, S., Shaw, G., Star, A., Vidgen, H., Leveritt, M., ‘Sports Dietitians Australia Position Statement: Sports nutrition for the adolescent athlete’, International Journal of Sports Nutrition and Exercise Metabolism, 2014, 24(5):570–84.
  7. Nicol, L; Sports and exercise physician, Christchurch NZ, Personal communication Aug 2021

About the author View all

Lea Stening

Lea is one of New Zealand’s leading paediatric dietitians and also specialises in Sports Nutrition. She has specialised in Paediatric Nutrition for 31 years and in 1985 was the first paediatric dietitian to enter private practice in New Zealand. Lea helps families through her private consultations, public lectures, newspaper and magazine articles as well as television and radio interviews. Read more »

View all posts by Lea Stening »


Leave a Reply

Also in Diet Therapy View all »

  • Dietary Guidelines are constantly changing:...

    Although science is constantly evolving, generating new recommendations to improve our health, for many people their eating habits are based on things other than their longevity so are guidelines still relevant today? Read more »

  • Break free from Fad Diets

    New diets pop up every day. Who should we believe? NZ Broadcasting student Louise Trenouth, on assignment, puts questions to Lea in an effort to understand Fad Dieting. Read more »

  • How to make the most of a plant-based diet

    The plant-based diet is widening the range of foods on our supermarket shelves. How do they compare with standard meat and dairy products for nutrition value? Find out.. Read more »

  • Healthy At Every Size (HAES): the debate

    The Healthy at Every Size (HAES) paradigm, focusing on body acceptance and healthy lifestyle changes, is gaining a lot of media attention as a possible way of curbing our escalating obesity stats. Find out more. Read more »

  • Are you afraid of the scales?

    Everyday we measure things such as the time, money, distance, our cholesterol, petrol etc yet many people fear measuring themselves Read more »

  • Stay in ‘the loop’ for a brighter...

    Loneliness and social isolation are being increasingly seen as risk factors to good physical and mental health. Learn how to stay connected with others and improve your sense of well being in 5 easy steps. Read more »

  • Unlock your potential with food

    The power of food can change your life and Dietitians can help you unlock your potential through food. Read more »

  • 10 Tips for better food choices this Christmas

    Weight control is the key to better health but this can be hard when Christmas often leads to overconsumption. Find out where to start. Read more »

  • Dietitians and Nutritionists what’s the...

    Dietitians are the most credible source of nutrition and food knowledge when you need to apply it to health and disease in NZ. Read more »

  • Wise up to Discretionary Foods for better health

    If you are struggling to lose weight or lower your cholesterol then taking a closer look at your intake of discretionary foods can improve your results. Read more »

  • How to put ‘real’ flavour into...

    It can be so easy to snip the top off a packet of flavouring when cooking. But if we really want to reduce the salt, fat and sugar in our diet natural flavours are best. Find out how. Read more »

  • Dietary help for women with PCOS

    Polycystic ovarian syndrome (PCOS) is a common cause of infertility in 6-20% of women of reproductive age causing a range of hormonal and metabolic effects that can impact on a women's physical and mental health. Read more »

  • Garnishes galore and all those “little...

    Is garnishing getting out of hand? Find out how much energy those "add ons" really do add. Read more »

  • 7 Myths about weight loss

    Lea Stening shares 7 common myths about weight loss and concludes that "you actually need to eat quite a lot of food in order to lose weight". Read more »

  • Time your eating for better performance?

    If playing sport or exercising, understanding the GI can help you to select foods that will provide optimal energy at key stages of activity for better performance. Read more »

  • Tips to help you ‘shake off’ the...

    In a bid to reduce the intake of processed foods many food manufacturers are modifying their products to meet new food guidelines particularly regarding salt. Find out if you are still getting too much? Read more »

  • Is going “Gluten Free” a healthy...

    As the popularity of gluten- free diets grow we need to question whether in fact it is a healthy option for any of us and if not how can we make it so? Read more »

  • Does your diet tick all the boxes?

    Is dieting still fun if it ages you? Find out if your diet ticks all the boxes for your better health and performance. Read more »

  • 10 tips to prevent weight gain in marriage

    When couples move in together they set in motion changes to their long-term health. While there are many health benefits of living together managing weight may need extra care and attention Read more »

  • Don’t let energy deficiency ruin your health

    Energy deficiency is not just a problem of third world countries. It can be found in our hospitals, schools and kindergartens, rest homes and on our sports fields. It can affect over and underweight people. Read more »

  • Sports supplements should be taken with care

    While some supplements are well recognised as being useful to performance others can lead to positive drug testing and disqualification as well as endanger long-term health. Read more »

  • Changing our “weight talk” may...

    A child can build their confidence and self esteem if monitoring their growth rate is accompanied by positive health messages about weight, fitness and energy to achieve in life. Read more »

  • Don’t let stress fractures slow your...

    Stress fractures are not just a problem for athletes who overtrain. They can affect anybody as they also relate to lifestyle and nutrition choices. Find out if you at risk. Read more »

  • Nutrition for distance runners and “fun runs”

    Distance running and “fun runs” (and walks) of varying length and degree of difficulty are becoming popular, attracting family and community groups; recreational and elite participants. Paying attention to sports nutrition can improve an athletes performance and enjoyment of these events Read more »

  • Juice diets – are they as healthy as...

    For busy people, who might rather drink than chew their fruits and vegetables, the juicing trend sounds like a "gods send". What possible disadvantages could there be to health? Find out the pros and cons of this new diet craze. Read more »

  • Driving for a living? 10 tips to help your...

    Spending hours behind the wheel is a huge recipe for weight gain and increased risks to our health. Driving is something that affects us all. Read more »

  • Feeling full is the secret to weight loss

    Gaining an understanding of the many factors contributing to a sense of fullness can provide some very powerful tools for those seeking to lose or control body weight and find more energy for life! Read more »

  • Can coconut improve our health?

    Coconut oil was once associated with tanning. Something young people coated themselves with before lying out in the sun “to bake”. Today coconut products are being heralded by many as the new “wonder food" that can cure many ailments. We take a look at some of these claims. Read more »

  • Dietary help for depressed athletes

    Although athletes may benefit from an exhilarating endorphin rush on exertion that elevates their mood and suppresses feelings of pain it will not stop them from experiencing, at times, anxiety and bouts of depression just like the rest of us. Nutrition is one treatment option that can speed recovery. Read more »

  • Sugar control is essential for better health

    After years of encouraging a low fat diet with some success (a decline in heart disease and some forms of cancer) attention is now focusing on sugar as a possible reason for our weight and diabetic problems. Read more »

  • Boosting fibre intake offers health benefits

    Research shows that a diet high in fibre can reduce the risk of developing diseases such as type 2 diabetes, coronary heart disease, bowel and breast cancer, gallstones, diverticular disease and weight gain. It also seems that some fibres are better than others. Read more »

  • Diet can offer protection when cold conditions...

    Cold injuries and illness occur in a wide range of physical activities. An understanding of the importance of sports nutrition and planning appropriate meals and snacks can offer some protection and may also improve overall performance Read more »

  • Healthy diet aids menopause management

    Menopause is a natural biological process women pass through and just like puberty it is not a medical illness. A woman's experience of Menopause is very individual and so there is no one "cure" for the range of symptoms that may be experienced. Read more »

  • Could the French Diet reduce obesity in New...

    The French diet is relatively high in saturated fat and yet in 2012 the French have a low incidence of obesity (11% compared to 28% in New Zealand). Why is this? Read more »

  • How to increase the ‘Good’ fats...

    If you are thinking of cutting fat out of your diet stop right now. Fat is important for nerve and cellular function but choosing the right “type” of fat is what matters most to our long term health. Read more »

  • Can a high fat diet improve sports performance?

    Fat carries more energy than other macro nutrients (9kcals/37kJ/g compared to 7kcal/29kJ/g for alcohol and 4kcal/17kJ/g for protein and carbohydrate respectively). So with so much energy to offer does eating more improve performance? Read more »

  • Healthy ideas for family takeaway meals

    Did you know that in 2012 around 21% of New Zealander’s weekly food expenditure was spent on eating out and takeaways? Read more »

  • Are you a “sneaky snacker”?

    Some people find it hard to control snacking and are continuously thinking about food. They may find themselves constantly picking, stock piling foods in drawers and cupboards at home and work. Read more »

  • Vegetarians face extra hurdles

    Despite the apparently healthier lifestyle vegetarian athletes (like anybody) can still become overweight, hungry, bloated and suffering from multiple nutrient deficiencies. Read more »

  • The gut-brain axis is important to sporting...

    Do you ever suffer from” runners diarrhoea”, bouts of anxiety , fatigue, abdominal pain or gas when facing competition? Read more »

  • Swim for your life

    Whether you are swimming for fun or competition this sport has many health benefits that can be enhanced with good nutrition. Knowing what to eat and when can also greatly improve your enjoyment of the sport as well as your level of performance. Read more »

  • Eat your way to healthier nails

    The quality, appearance and growth of our nails often reflect the state of our general health and the adequacy of some essential nutrients in our diet. Read more »

  • Skin care for active people

    The stress of competition, the sun and wind, sweat, chaffing and high sugar levels are just some of the things that can aggravate the skin conditions of athletes and very active people. Read more »

  • Care for “the carers” during family...

    When family members are sick or hospitalised it can be very challenging to find the time to exercise and maintain a healthy diet for yourself. Particularly if you are working, caring for children, or trying to complete a course of study. Read more »

  • Don’t let disordered eating ruin your...

    An eating disorder can affect anyone at any age, any sport, any background and any gender. The symptoms may build slowly well before the illness becomes evident. Often it is an athletes support team such as parents, friends, team mates and coaches that pick up on the symptoms and can prevent the disorder from ruining the athletes sporting career. Read more »

  • Could your weight be disabling you?

    The human body is hugely resilient, constantly strengthening muscles and remodeling bones and joints to take up new loads. However as we age and weight is gained and lost, metabolic changes can take place that alter this remodeling process and can set us on a path to failing mobility and independence. Read more »

  • Obesity problems may start in the womb

    Overweight and obese women are a greater risk of developing complications endangering their own health during pregnancy and are also more likely to bare children who are overweight themselves Read more »

  • Put Sports Nutrition to work

    Many workers use enough energy and essential nutrients each day to power a marathon. If not replaced then a lack of these key nutrients can lead to fatigue, accidents and injury that can affect their long-term health and mobility. Read more »

  • Athletes protect your winning smile

    Athletes protect your smile and your wallet as painful tooth erosion is not only expensive it can also rob your training time and performance. Read more »

  • 8+ Tips for managing teething troubles

    Few children escape teething without some discomfort. Rosy flushed cheeks, a runny nose, irritable behavior, disturbed sleep and bowel function are all hallmarks of tooth eruption Read more »

  • Facing the down times without weight gain

    Nothing can be more infuriating for an athlete than after months of intense training an injury sees you ‘sidelined’. Read more »

  • Sports nutrition for women

    Women who push the boundaries of their lives to take on new challenges and sporting events are usually also trying to juggle their work, home and training existence. With good sports nutrition advice It is possible to find renewed energy. Read more »

  • Who controls feeding – the mother or the...

    Studies of toddlers aged 20 months to 6 years, that examined baby-led weaning versus traditional spoon feeding methods have found that feeding method can influence food preferences and health related outcomes in later life. We look at the pros and cons. Read more »

  • Sports nutrition for cycling

    Cycling tests an athlete’s strength and endurance capabilities as well as their anaerobic energy systems during breakaways, hill climbs and sprints to the finish.While some athletes rely heavily on dietary supplements, these will not replace a healthy training diet that is high in carbohydrate, with moderate protein and low in fat. Read more »

  • The protein needs of young athletes

    At a time when they are also growing, young athletes may need as much as 50% more protein than their more sedentary peers. Read more »

  • Food to Fuel the Speights Coast to Coast

    Whether you are a novice or seasoned triathlete your nutrition plan could make or break your race. All those competing should read the excellent nutrition tips on the official Speight’s Coast to Coast website and seek professional help if they have any concerns. In addition here is a check list of things you should also consider. Read more »

  • Children’s bone growth and gut health...

    Every parent wants their children to grow. But the height that they finally reach is dependent on factors such as growth hormone, genetics and nutrient availability. While we can’t change genetics after their arrival or growth hormones easily, nutrient availability can make the difference and is something parents can influence and need to be more … Read more »

  • Nutrition for tendons and ligaments

    The recent Rugby World Cup has placed the spot light on sports injuries and so we thought it might be interesting to look more closely at the protective role of sports nutrition and in particularly the nutrients important to tendon and ligament health. Read more »

  • Brace yourself for the brassicas

    With Winter now upon us its time to eat more Brassica vegetables. What are they? Broccoli – 7th most popular vegetable in New Zealand Cauliflower – 13th most popular Cabbage (all types) – 12th most popular Brussel Sprouts Broccolini – consumption rocketing! Swedes Turnips Why are they so good? Brassicas contain: Antioxidants, from the following … Read more »

  • Infant nutrition influences blood pressure...

    Scientific evidence suggests that environmental factors acting early in life may affect blood pressure in adult life. A study in Britain in 2004 supported earlier studies on infant nutrition and blood pressure that show a small reduction in systolic blood pressure in children breast-fed compared to those who were bottle-fed. Other advantages of breastfeeding Breast … Read more »

Would you like to subscribe to our fantastic FREE monthly newsletter?

Each month we'll keep you up-to-date with the latest nutritional articles and healthy recipes from You are free to opt out at any time, but we think you'll enjoy what we've got in-store for you.

Plus as a bonus offer — subscribe today and receive FREE weight loss tips for two weeks! Learn how a number of foods, many one would consider 'healthy', may in fact be slowing your progress.


Yes please, it sounds great! (and it's FREE after all).



No thanks, I'm not interested (or I'm already a subscriber and really enjoying these fantastic newsletters!).