- Have you ever wondered about the seasonal variation in colds and flu’s?
- Why is influenza seasonal in every country?
- Given the amount of international travel, why doesn’t the flu hit both hemispheres at the same time?
- Why do epidemics occur coincidentally at the same latitudes?
- Where is the virus between epidemics?
Have a look at the following graphs. Because I’m in New Zealand I’m using data from our country – you will find however the exact opposite pattern if you live in the northern hemisphere. The highest ‘flu rates are in August. They are very low in the summer months November – March.
Compare this to the levels of vitamin D measured in blood samples in labs in Auckland (22,000 Auckland adults, 25 (OH) D by age)
You may have noticed that the decrease in blood vitamin D is the exact opposite of the flu rates. This pattern of low vitamin D coinciding with high rates of flu occurs worldwide.
This suggests we should make sure we have blood vitamin D levels of at least 60nmol/ L during the winter to reduce risk of colds and flu. Most researchers now consider 50nmol/L (20 ng/ml) to be the absolute minimum, and 75 – 100 nmol/L to be more optimal (30 – 40 ng/ml)
So would it be smart to supplement with Vitamin D3?
Studies suggest yes.
Supplementation in Japanese school children
This was a randomized controlled study, 167 children in each group, the vitamin D group received 1200IU D3 per day, the other group a placebo.
Children received the supplement from December 2008 – March 2009 (the Japanese winter)
Influenza A occurred in 18 / 167 vit D group, and 31 / 167 placebo group
Asthma attacks were also reduced: 2 children in Vit D3 group had asthma attacks vs 12 in placebo group.
Mongolian School children study
247 children, received either vitamin D fortified milk (300iu) or plain milk
Those who received Vit D had half the risk of upper respiratory infection. Vitamin D levels increased to a mean of 47 nmol/l from a baseline of 20nmol/l
Adults with impaired immunity and frequent respiratory tract infections, Sweden
140 patients who suffered several respiratory tract infections every year, many of whom required antibiotics. Patients were randomized to receive 4000IU vitamin D3 or placebo daily for 12 months. Each person documented every respiratory infection and the number of times they had to take antibiotics. Nose and throat swabs were taken with every infection.
Results: 25 (OH) D levels rose from 50nmol/l to 133 in treatment group. The vitamin D3 group had 76 positive microbial swabs (bacteria or fungi) vs 159 in the placebo group. There was significantly less fungi (Candida spp. and Aspergillus spp.) and bacteria: S Aureus.
At 12 months no pathogens could be detected in nasal swabs of vitamin D3 group, whereas the placebo group continued to show both normal and abnormal flora.
The amount of antibiotics taken by treatment group was 60% less than placebo group.
Another interesting documented result was less adverse events in the Vitamin D3 group. Significantly more patients in the placebo group reported cardiovascular problems, such as heart failure and thrombosis, as well as higher rates of non respiratory infections.
How much vitamin D should you take?
In the summer, build up your vitamin D3 levels by exposing skin around the middle of the day, without sunblock. Just a few minutes exposure is enough for those with light colour skins, up to 30 minutes for those with darker skins. In the winter supplement with 1000 to 4000IU per day. To check your Vitamin D levels, you can go directly to Labtests (New Zealand) and pay for it – around $45.00. People respond differently to supplementation so this will allow you to see how much you need to take to build your levels to between 30 – 40 ng/mmol or 75 – 100 nmol/L.