On the 22 October I mentioned the potential use of Vitamin D supplements for helping individuals suffering from the mood disorder SAD (seasonal affective disorder).  This year a number of papers have been published (1,2,3,4) which suggest that vitamin D could potentially be useful for the treatment of other mood disturbances and depressive episodes.

In 2007 a review paper was published (5) which suggested that vitamin D deficiency may play a role in depression and other mood and mental health disturbances, especially in the elderly where low vitamin D levels are commonly found.  The paper highlighted a number of trials that which showed that vitamin D supplementation appeared to be useful in the treatment of depression but expressed a need for further studies.

Vitamin D seems to be a hot topic this year and I have written about it a number of times in my blog posts.  Low vitamin D levels seem to be linked to cancer, heart disease, SAD, chronic fatigue syndrome, migraine headaches and various other diseases, not only bone conditions such as osteoporosis and osteoarthritis.  It is becoming glaringly obvious that this ‘sunshine vitamin’ is more important than we once thought. 

Two studies this year have linked low vitamin D status, as measured by low circulating blood levels of vitamin D, with depressive symptoms.  One study (1) was carried out in overweight and obese individuals and the other (3) in older adults (aged 65 – 95 years).  Both studies found that there was an association between depression status and severity with decreased serum (blood) vitamin D levels.  In the study with overweight/obese participants high-dose vitamin D supplementation led to significant improvements in depressive symptoms, compared to placebo, during the study.  The studies so not prove a causal relationship between low vitamin D and depression but they do add to the mounting evidence which suggests a very real link.  Further, larger studies will be needed to verify the information and investigate this exciting association further.

It is not currently known why vitamin D may be useful in treating mood disorders or why low levels may have a part to play in causing mood problems.  It may be that vitamin D has an effect on hormones linked to mood.  Studies are bound to unravel the mystery over the next few years!

A recent analysis(6) found that there is a global widespread insufficiency of vitamin D and there is evidence from the National Diet and Nutrition Surveys (NDNS) which suggests that in the UK deficiency of this vital nutrient is a real problem (7,8,9,10).  The problem is made worse in the older generations, as we age our bodies find it increasingly difficult to manufacture vitamin D.  In the UK many of us do not get enough sunlight exposure to generate decent levels of vitamin D in our bodies, especially in the autumn and winter months when we cover our bodies up and don’t get out during the daylight hours very often. 

Walking and exercise have also been linked to improved mood, so a lunchtime walk, in daylight, may bring added mood lifting benefits.  Only small amounts of vitamin D are found in food sources such as oily fish (mackerel, salmon and sardines) and eggs.  As many of us in the UK are falling short of recommended vitamin D levels, if you rarely get out into the sun, you may wish to consider a vitamin D supplement which provides around 12mcg/day (around 500iu a day).  Such a supplement may be particularly useful during the autumn and winter months.

You may also want to think about getting a daylight lamp for your work desk to help improve mood.  Some of these lamps produce light that the body can use for vitamin D production (check with the manufacturer of the lamp).

For more interesting information about the benefits of vitamin D and sunlight for health please visit the Sunlight Nutrition And Health Research Centre, the information there is well presented and backed up by significant amounts of good evidence.

(1)Jorde R et al.  2008.  Effects of vitamin D supplementation on symptoms of depression in overweight and obese subjects: randomized double blind trial.  J Intern Med. Sep 10. [Epub ahead of print]
(2)Murphy PK & Wagner CL.  2008.  Vitamin D and mood disorders among women: an integrative review.  J Midwifery Womens Health.  53:440-446
(3)Hoogendijk WJ et al.  2008.  Depression is associated with decreased 25-hydroxyvitamin D and increased parathyroid hormone levels in older adults. Arch Gen Psychiatry. 65(5):508-12.
(4)Johnson MA et al.  2008.  Vitamin D deficiency and insufficiency in the Georgia Older Americans Nutrition Program.  J Nutr Elder.  27:29-46
(5)Berk M et al.  2007.  Vitamin D deficiency may play a role in depression.  Med Hypotheses.  69:1316-1319
(6)Hagenau T et al.  2008.  Global vitamin D levels in relation to age, gender, skin pigmentation and latitude: an ecologic meta-regression analysis.  Osteoporosis International May [E publication ahead of print]
(7) Finch S et at.  1998.  National Diet and Nutrition Survey of People aged 65 Years and Over.  London: H. M. Sationery Office.
(8) Gregory L et al.  2000.  National Diet and Nutrition Survey of People aged 4-18 years. Vol 1.  Report of the Diet and Nutrition Survey.  London:  The Stationery Office
(9) Henderson L et al.  2002.  National Diet and Nutrition Survey: Adults Aged 19-64 years.  Vol 1: Types and Quantities of Foods Consumed.  London: The Stationery Office
(10) Hypponen E & Power C.  2007.  Hypovitaminosis D in British adults age 45y: nationwide cohort study of dietary and lifestyle predictors.  Am J Clin Nutr.  85:860-888.

Written by Ani Kowal

Continuing on from from Part I here are some more ideas for SAD (seasonal affective disorder) sufferers, or for anyone wishing to lift their mood in the autumn and winter months.

Exercise
Numerous studies point toward the general mood enhancing effects of exercise.  A 30 minute walk during the day may help to lift the mood.  Studies specifically investigating SAD have found that light therapy in conjunction with daily exercise seems highly beneficial in reducing SAD symptoms (1,2,3).  There seems to be an apparent additive effect of exercise and light on mood and health-related quality of life in individuals suffering with SAD.  Trying to get out for a lunchtime walk, when the light is at its best in the winter, may really help to lift mood.  Walking with a friend can help motivation and provide time for talking which can help clear the mind.

Vitamin D
A review was published earlier this year (4) which looked at the association between vitamin D and mood disorders in women.  The researchers reviewed published study data and found that there was an association between low vitamin D levels and higher incidences of seasonal affective disorder (as well as major depressive disorder).  The authors conclude that further studies are warranted in order to asses the association in more detail.

I have previously mentioned that in the UK many of us do not get enough vitamin D.  Supplementation with vitamin D may be useful to improve mood in SAD sufferers (5,6).  It has been suggested that the seasonal symptoms of SAD may be due to changing levels of vitamin D3, the hormone of sunlight, and that supplementation with vitamin D may lead to positive changes in brain serotonin levels (a ‘feel-good’ brain chemical).  In one study subjects were given 400 IU, 800 IU, or no vitamin D3 for 5 days during late winter.  Results showed that vitamin D3 significantly enhanced positive feeling and there was some evidence of a reduction in negativity (5).  In another study, 30 days of treatment with vitamin D proved highly effective in resolving depression in a group of SAD sufferers (6).  Taking 400-800IU daily may be helpful to SAD sufferers during the winter months when sunlight is scarce.

Good diet, food cravings and blood sugar balance
Carbohydrate cravings are often reported by individuals suffering with SAD.  This could be due to the fact that carbohydrate increases the uptake of an amino acid (building blocks of protein) called tryptophan.  Tryptophan is used in the synthesis of serotonin, the good mood brain chemical.  If serotonin levels are good then appetite is often normalised and cravings are less likely occur. 

Regulating blood sugar levels with diet may also be helpful to SAD sufferers with disordered eating and cravings.  I wrote about this in more depth on the 8th and 10th of September.  Balancing blood sugar levels through eating a healthy diet that provides a slow and steady supply of energy throughout the day may help to prevent cravings and fatigue.  A diet rich in vegetables and fruits, healthy fats (especially omega 3 fatty acids from oily fish, fish oil or flax seed oil supplements) and proteins (from nuts/seeds, eggs, lean unprocessed meats, fish and pulses/beans) may help to minimise blood sugar imbalances and cravings.  Vegetables and fruits are great sources of unrefined carbohydrates as are wholegrains with a low glycaemic index (GI).  Please read my previous posts for more detail on glycaemic index and eating to minimise cravings.  If you feel that your diet is inadequate you may wish to consider taking an omega 3 fatty acid supplement (a fish oil or flaxseed oil supplement) and a good quality multivitamin-mineral supplement (I prefer ‘food state’ supplements).

Women suffering from the eating disorders bulimia or binge eating disorder may find that their conditions are more difficult to control in the winter time.  There is some indication (7) that light therapy can help minimise these symptoms in autumn/winter and aid mood and carbohydrate craving.  Investing in a light box or daylight alarm clock may prove useful.  For help and information on eating disorders please visit the BEAT website.  BEAT is a charity (the working name for the Eating Disorders Association) for people with eating disorders and their families.

Cognitive behaviour therapy / counselling
Finally, if you feel distressed and unable to cope with the depressive/mood symptoms associated with SAD you may well want to look at a form of counselling called Cognitive Behaviour Therapy to help.  There is indication (8) that this form of therapy is very useful in individuals dealing with SAD and low mood in winter.  For more information and useful links please visit the Royal College of Psychiatrists. 

Wishing you all a happy winter!

(1)Leppamaki S et al.  2004.  Drop-out and mood improvement: a randomised controlled trial with light exposure and physical exercise.  BMC Psychiatry.  4:22
(2)Partonen T et al.  1998.  Randomized trial of physical exercise alone or combined with bright light on mood and health related quality of life.  Psychol Med.  28:1359-1364
(3)Leppamaki SJ et al.  2002.  Bright light exposure combined with physical activity elevates mood.  J Affect Disord.  72:139
(4) Murphy PK&Wagner CL.  2008.  Vitamin D and mood disorders among women: an integrative review.  J Midwifery Womens Health. 53(5):440-6.
(5) Lansdowne AT et al.  1998.  Vitamin D3 enhances mood in helathy subjects during winter.  Psychopharmacology.  135(4):319-323.
(6)Gloth FM et al.  1999.  Vitamin D vs broad spectrum phototherapy in the treatment of seasonal affective disorder.  J Nutr Health Aging.  3:5-7
(7) Lam RW et al.  2001.  An open trial of light therapy for women with seasonal affective disorder and comorbid bulimia nervosa. J Clin Psychiatry.  62(3):164-8
(8)Rohan KJ et al.  2007.  A randomised controlled trial of cognitive behaviour therapy, light therapy and their combination for seasonal affective disorder.  J Consult Clin Psychol.  75:489-500

Written by Ani Kowal

World Osteoporosis Day occurs on Monday October 20th and the National Osteoporosis Society (NOS) is running a UK-wide campaign ‘Love Your Bones’ which is intended to raise awareness about the importance of healthy bones.  The goal of the National Osteoporosis Society is to improve understanding of osteoporosis, what causes it and to promote the steps people can take to keep their bones healthy and reduce their risk.

“Osteoporosis literally means ‘porous bones’. Our bones are made up of a thick outer shell and a strong inner mesh which looks like a honeycomb made up of tiny struts of bone. Osteoporosis means some of these struts become thin or break, making bones more fragile and prone to fracture. It often remains undetected until a bone is first broken, which commonly occurs in the wrists, hips and spinal bones. It is these broken bones or fractures which can lead to the pain associated with osteoporosis. Spinal fractures can also cause loss of height and curvature of the spine.”(1)

Please visit the NOS for loads more information on bone health.  They have many online and downloadable resources, including a booklet ‘Healthy Eating For Strong Bones’ and a page dedicated to the ‘Sunlight Campaign’ which highlights the fact that sunlight is one of the very best natural sources of vitamin D, a vitamin that is essential for the building of healthy bones and the prevention of osteoporosis.  The NOS point out that up to 15 % of people in the UK are estimated to have low levels of vitamin D, while 80% have levels which are considered unhealthy.  There have now been many calls for a revised vitamin D intake recommendation in the UK(2) due to extensive evidence of low levels. The NOS website provides simple tips for boosting your vitamin D levels.

Calcium and Vitamin D
A recent review paper(2) looked at the evidence surrounding the importance of calcium and vitamin D for bone health and the prevention and treatment of osteoporosis.  The paper points out that an estimated one in three women and one in twelve men aged over 55 years will suffer from osteoporosis in their lifetime.  This represents a huge cost in the UK (many millions of pounds per year).  Calcium supplements appear to be effective in reducing bone loss in women in late post menopause (after five years), particularly in those with a low daily calcium intake (less than 400 mg/d).  Supplementation with vitamin D and calcium has also been shown to reduce fracture rates in some elderly populations. Low vitamin D status is associated with an increased risk of falling and a variety of other health outcomes and is an area that requires urgent attention.

It is very important to consider bone health at an early age, this is because peak bone mass (peak bone strength) is reached before the age of 30, after this age bone gradually grows weaker.  Building up great bone strength early on in life will help reduce the risk of osteoporosis later in life.  Most studies show that calcium, supplemental or high dietary intake, is important in at a young age in order to reach a good peak bone mass (3), 600mg-1,000mg calcium daily before the age of 25 may be beneficial to reaching a good bone mass.  As mentioned above evidence regarding supplementation later in life is mixed.  However, a supplement containing vitamin D and calcium could be useful in maintaining bone mass (providing around 800mg calcium daily and 20mcg/800IU vitamin D).

Other nutrients
The role of other nutrients on bone remains to be fully defined(2), although there are promising data in the literature for links between various nutrients including: magnesium, zinc, copper, potassium, silicon, manganese, vitamin K, vitamin C, vitamin B and phytonutrients (biochemical plant compounds).  A varied, healthy diet, especially on rich in fruits and vegetables, will provide a huge array of nutrients that may positively impact bone health.  If you feel your diet is lacking you may wish to consider a high quality food-state multi-vitamin and mineral supplement.  This is NOT a substitute for good dietary habits!! 

Omega 3 fatty acids
Yes, it is the fish oils making an appearance again!  Eating a diet rich in the omega 3 fatty acids EPA and DHA, found in oily fish such as mackerel, salmon and sardines, may contribute to a reduced risk of osteoporosis by inhibiting the production of pro-inflammatory chemicals (eicosanoids) that are known to be involved in the process of bone loss.  This is a relatively new field of interest in osteoporosis.  Two recent reviews (4,5) looked at the evidence so far which does indicate a benefit, though the authors point out that further evidence is needed before firm conclusions can be drawn.  However, due to the numerous health benefits of omega 3 fatty acids (see previous blog posts) I would suggest the regular inclusion of oily fish in the diet (at least twice weekly), or taking a supplement providing around 250mg EPA and 250mg DHA a day.  For vegetarians I would suggest a daily flaxseed oil supplement to provide around 500mg alpha-linolenic acid (a shorter chain omega 3 fatty acid).

Fruits and Vegetables
A number of studies over the last decade have suggested a clear, positive link between fruit and vegetable consumption and bone health(6).  These foods provide a huge range of nutrients that are important for bone health.  In addition to the nutrients fruit and vegetables positively affect the pH balance (a measure of acid-alkali balance) in the body, by increasing the alkalinity in the body (making the body less acidic), which plays a major role in the prevention of calcium loss from bones.  Foods which are acid forming in the body include foods such as most meat and animal protein, cheddar cheese and many grain products e.g. white bread, pasta, cornflakes.  If the body is too acidic, not in pH balance, then bones can release their calcium (which increases alkalinity) into the blood to try and maintain the balance.  Obviously calcium loss is not what we want!!  Providing the body with abundant supplies of vegetables and fruits may well help to keep our bones strong as well as protecting us from many other diseases.

If you drink a lot of caffeinated tea, coffee or regularly consume fizzy drinks you may wish to reduce the amount you consume in order to protect your bones.  High intakes of these drinks can have a negative effect on bones.  The phosphoric acid they contain may cause calcium loss from bones.

Visit the National Osteoporosis Society website for more information

(1)The National Osteoporosis Society
(2) New-Lanham SA.  2008.  Importance of calcium, vitamin D and vitamin K for osteoporosis prevention and treatment.  Proc Nutr Soc.  67(2):163-76.
(3) Eastell R & Lambert H.  2002.  Strategies for skeletal health in the elderly.  Proc Nutr Soc.  61:173-180
(4)Salari P et al.  2008.  A systematic review of the impact of the impact of n-3 fatty acids in bone health and osteoporosis.  Med Sci Monit.  14:RA37-44
(5)Fernandes G et al.  2008.  Effects of n-3 fatty acids on autoimmunity and osteoporosis.  Front Biosci.  13:4015-4020
(6) New SA.  2003.  Intake of fruit and vegetables:implications for bone health.  Proc Nutr Soc.  62:889-899

Written by Ani Kowal

On Thursday (19th June) the American Medical Association (AMA), the largest doctors organisation in the USA, voted at their Annual Meeting to urge the Food and Drug Administration to re-examine the recommendations for vitamin D intake in light of new scientific evidence.

Those of you who have been reading my posts will know that I have mentioned vitamin D a couple of times already with respect to prevention of many diseases including cancer and heart disease.  This year alone there have been over 100 papers, articles or studies released which show how important this ‘sunshine vitamin’ is for our optimal health and wellbeing.  There is an almost constant stream of new scientific findings showing benefit.

The AMA are concerned because the American Reference Intake Values for Vitamin D were established back in 1997.  I hope that here in the UK we follow suit soon and re-examine our recommended intake too.  Ours was set back in the early 1990s!  Current research strongly suggests that we need more of this important vitamin than previously thought.

On Friday (20th June) a study(1) was published in the Journal of Clinical Oncology, I wanted to mention it here because it did not look at vitamin D with regards disease prevention.  The study looked at vitamin D and survival after cancer.  It has been previously shown that individuals with higher levels of vitamin D in their blood are less at risk of contracting colorectal cancer.  This present study found that among patients affected by colorectal cancer a higher pre-diagnosis vitamin D level was associated with a significant improvement in overall survival.  The authors of the study say that a trial is being planned in which colon cancer patients will take vitamin D along with post-surgery chemotherapy to assess whether there are any benefits with supplementation.

Just as I was about to finish this post a very interesting piece of peer-reviewed clinical research came to light(2) that was published in Pain Treatment Topics a few days ago.  The paper looked at vitamin D in relation to ‘pain’ and found that:

“Inadequacies of vitamin D have been linked to chronic musculoskeletal pain of various types, muscle weakness or fatigue, fibromyalgia syndrome, rheumatic disorders, osteoarthritis, hyperesthesia, migraine headaches, and other complaints. It also has been implicated in the mood disturbances of chronic fatigue syndrome and seasonal affective disorder.  Current best evidence demonstrates that supplemental vitamin D can help to resolve or alleviate chronic pain and fatigue syndromes in many patients who have been unresponsive to other therapies.”

There are downloadable documents on the Pain Treatment Topics website which provide detailed background information and recommendations.  There is a Full report and a Patient brochure available.  If you are suffering from any of the mentioned conditions you may wish to discuss this evidence with your doctor to see if Vitamin D supplementation could be useful to you.

Many of us find that spending some time in the sunshine is very healing for the mind and helps to reduce perceived stress-levels too.  It really does seem like the sun is important for the health of the body too!

(1)Ng K et al.  2008.  Circulating 25-Hydroxyvitamin D Levels and Survival in Patients With Colorectal Cancer.  Journal of Clinical Oncology.  26(18):2984-2991
(2) Stewart B. Leavitt, MA, PhD, Pain Treatment Topics, June 2008.  Vitamin D – A Neglected 'Analgesic' for Chronic Musculoskeletal Pain.  An Evidence-Based Review & Clinical Practice Guidance

Written by Ani Kowal

On the 30th May  I wrote about the importance of Vitamin D for health and concentrated mainly on the link to cancer prevention.

Yesterday a study was published in the Archives of Internal Medicine(1) which adds to the growing body of research that links low vitamin D levels to poorer heart health.

This particular study involved a group of 18225 middle aged and older men (aged 40-75 years).  The men were free of diagnosed heart disease at the initial blood collection.  They were then followed for 10 years and in this time 454 developed heart attacks (which were either fatal or non fatal).  The study scientists then compared the blood levels of vitamin D in those men who had suffered a heart attack to a group of 900 similar men (matched for certain factors such as age and smoking status) who had not.  The results showed that men with low blood levels of vitamin D were at increased risk of heart attack compared to men with sufficient levels.  Even men with intermediate blood levels of vitamin D were at increased risk of heart attack.

The findings are significant as the scientists adjusted the results to exclude a whole host of other possible confounding factors such as family history of heart attack, weight (Body Mass Index), alcohol consumption, physical activity levels, history of diabetes, blood pressure, ethnicity, omega 3 fatty acid intake and cholesterol levels.  Even when these factors were taken into account the men with low vitamin D levels were twice as likely to experience a heart attack than those with high vitamin D levels.

The authors of the study conclude that “Low levels of 25(OHD) [vitamin D] are associated with a higher risk of myocardial infarction [heart attack] in a graded manner, even after controlling for factors known to be associated with coronary artery disease”

Previous studies have linked low vitamin D levels to atherosclerosis (hardening of the arteries), congestive heart failure and high blood pressure.  As I mentioned in my previous post on vitamin D many of us in the UK may not have adequate levels of vitamin D in our blood.  A supplement of 12mcg/d (around 500iu) could be useful to those who rarely get out in the sunlight or during the autumn and winter months.

It is not entirely understood why vitamin D is so important for the health of the heart.  There are indications that vitamin D acts to reduce the production of pro-inflammatory chemicals (cytokines) which are linked to heart disease and may even increase the production of anti-inflammatory chemicals which are protective.  Vitamin D may also have an effect on certain hormones which play an important role in the regulation of blood pressure. 

(1)Giovannucci E et al.  2008.  25-Hydroxyvitamin D and risk of myocardial infarction in men: a prospective study.  Arch Intern Med.  168:1181-1187

Written by Ani Kowal

Vitamin D appears to be receiving a lot of attention in the scientific and medical press at present with well over 20 studies due for publication in June alone and many, many more already published in 2008.  In fact, as I started to research for this post the current issue of The Proceedings of The Nutrition Society arrived through my letterbox (Volume 67 No.2) and two of the featured papers covered the importance of vitamin D (one in relation to cancer and one in relation to the treatment and prevention of osteoporosis).

Vitamin D is called the sunshine vitamin, though technically vitamin D is a hormone, as it is produced in the body when the skin is exposed to the UVB rays in sunlight.  In theory spending just 10-15 minutes in the sun everyday should supply all the vitamin D that we need.  However, many of us do not get enough sun on our skin to generate adequate amounts of vitamin D especially in the autumn and winter months.  A recent analysis(1) found that there is a global widespread insufficiency of this vital nutrient and there is evidence from the National Diet and Nutrition Surveys (NDNS) which suggests that in the UK vitamin D deficiency is a real problem (2,3,4,5).  The problem is made worse in the older generations since, as we age our bodies find it increasingly difficult to manufacture vitamin D.

This does not make for good news since vitamin D is vital for our health.  Not just the health of our bones and teeth but a for our hearts (the vitamin may protect against atherosclerosis, heart attack and high blood pressure), our digestive systems, the immune system (there is increasing evidence to show that vitamin D is important in the prevention of cancer), blood sugar control (and the prevention of type I and type II diabetes and insulin resistance), muscles, brain (deficiency is linked to depression and mood), fertility and skin health.  Quite a list!

I would like to write a bit more about the link between vitamin D and cancer.  We are constantly told by the media to avoid the sun as it increases our risk of a certain type of skin cancer called ‘malignant melanoma’.  However evidence is now mounting to suggest that insufficient sunlight exposure and low vitamin D levels actually increase the risk of several types of internal cancers such as breast, prostate, colon, bladder, kidney, lung, pancreas and ovary (to name but a few) (6,7).  Just as I was finishing this post a study was published (8) which looked at UVB exposure, vitamin D levels and breast cancer risk across 107 countries.  The authors of the study found that higher blood vitamin D levels were associated with lower rates of breast cancer and UVB exposure had a protective effect on the risk of breast cancer (these effects were independent of potential confounding factors such as fertility rate, overweight, alcohol intake, animal energy intake).  Vitamin D seems to have many cancer protective properties;  it can prevent cells from multiplying and can also specifically induce the death of cancer cells. 

It certainly seems that the sun is very important for our optimal health and wellbeing!

It is essential to be safe in the sun and avoid getting burned and baked, malignant melanoma is a particularly nasty skin cancer.  However , the risk of this type of skin cancer is relatively low in comparison to other forms of cancers and staying out of the sun completely will probably do more harm than good with regard to health and overall cancer risk.  For more interesting information about the benefits of sunlight for health please visit the Sunlight Nutrition And Health Research Centre, the information there is well presented and backed up by significant amounts of good evidence.

The UV in sunlight is believed to be our main source of vitamin D with only small amounts being found in food sources such as oily fish (mackerel, salmon and sardines)and eggs.  Recently, however, there has been mass debate about whether UV exposure in the UK is sufficient to keep vitamin D levels optimal for health.  I mentioned earlier that most of us in the UK are falling short of recommended levels.  If you rarely get out into the sun you may wish to consider a vitamin D supplement which provides around 12mcg/day (around 500iu).  Such a supplement may be particularly useful during the autumn and winter months.

(1) Hagenau T et al.  2008.  Global vitamin D levels in relation to age, gender, skin pigmentation and latitude: an ecologic meta-regression analysis.  Osteoporosis International May [E publication ahead of print]
(2) Finch S et at.  1998.  National Diet and Nutrition Survey of People aged 65 Years and Over.  London: H. M. Sationery Office.
(3) Gregory L et al.  2000.  National Diet and Nutrition Survey of People aged 4-18 years. Vol 1.  Report of the Diet and Nutrition Survey.  London:  The Stationery Office
(4) Henderson L et al.  2002.  National Diet and Nutrition Survey: Adults Aged 19-64 years.  Vol 1: Types and Quantities of Foods Consumed.  London: The Stationery Office
(5) Hypponen E & Power C.  2007.  Hypovitaminosis D in British adults age 45y: nationwide cohort study of dietary and lifestyle predictors.  Am J Clin Nutr.  85:860-888.
(6) Grant WB.  2002.  An estimate of premature cancer mortality in the U.S. due to inadequate doses of solar ultraviolet-B radiation.  Cancer.  94:1867-1875
(7) Grant WB & Garland CF.  2006.  The association of solar ultraviolet B (UVB) with reducing risk of cancer: multifactorial ecologic analysis of geographic variation in age-adjusted cancer mortality rates.  Anticancer Research.  26:2687-2699
(8) Mohr SB et al.  2008.  Relationship between low ultraviolet B irradiance and higher breast cancer risk in 107 countries.  Breast J.  14:255-60

Written by Ani Kowal