Can You Predict Vitamin D Status Without a Lab Test?
Much has been written about the global epidemic of vitamin D deficiency. Yet, there is still a considerable lack of awareness of vitamin D deficiency in the general population. Perhaps this has something to do with the current range of tests available. Unlike other vitamins, skin synthesis after sun exposure is an important source of vitamin D, therefore the dietary analysis tools that can normally be used to estimate vitamin and mineral intakes are not useful for vitamin D. The current selection of options to measure vitamin D status include:
- Accurate but slow and expensive blood tests that can be done under the guidance of a doctor and require a venous blood sample, with results available within a few days from when the sample was taken
- Self-tests that use a minimally invasive blood spot from a finger prick done at home, results available in a few days
- Non-validated online tests in atrocious English that estimate vitamin D levels
- Pressure-pain thresholds on the breast bone or shin bone, which are only weakly correlated with vitamin D levels (see Dresser and colleagues).
Recently, Xu and co-workers looked at vitamin D levels in sub-tropical Hong Kong, China. They were primarily interested in seasonal fluctuations and their effects on vitamin D levels. They included blood samples from 2694 adult and child subjects, and among the children, a diet and lifestyle questionnaire was included to see if elements could be identified that affected vitamin D levels.
The authors found a 5-week delay between peak and trough sunlight intensity and vitamin D levels, that is, vitamin D levels were lowest around 5 weeks after the lowest solar radiation was measured. The results of the questionnaire in children provide results that could be used for a questionnaire to assess likelihood of vitamin D deficiency. While non-modifiable factors such as female sex and being a teenager were associated with lower levels of vitamin D, other modifiable factors were found. Having had a suntan in the past year, consuming fish, consuming milk and cod liver oil intake improved vitamin D status in the simple model, while egg consumption also improved vitamin D status is the adjusted model.
Interestingly, using sunscreen, recent sun exposure, use of a vitamin D or multivitamin supplement, and skin color were not associated with vitamin D levels. The reason for this may be that some of these behaviors lead to other changes in behavior that may counteract the expected effect. For example, people who wear sunscreen block the exposure of their skin to the sun, however people only wear sunscreen if they are going to be outside. The people who don’t wear sunscreen may be more likely to stay inside, where they will also not produce any vitamin D on their skin. Likewise with skin color, people with darker skin produce less vitamin D when exposed to the sun, however as they are also less likely to burn, they may spend more time in the sun.
We have reported on using questionnaires to predict vitamin D status in the past. Questionnaires offer us a low-cost way to predict who is at risk of vitamin D deficiency. Blood tests are better, but have some drawbacks. Personalized nutrition is coming. For now, we have questionnaires.
Cuiling Xu, Ranawaka A. P. M. Perera, Yap-Hang Chan, Vicky J. Fang, Sophia Ng, Dennis K. M. Ip, Andrea May-Sin Kam, Gabriel M. Leung, J. S. Malik Peiris and Benjamin J. Cowling. British Journal of Nutrition. Published online: 08 June 2015. http://dx.doi.org/10.1017/S0007114515001683
Dresser J, MacIntyre M, Chisholm B, Lawson GE. Is bone tenderness, as measured by manual algometry, associated with vitamin D deficiency? The Journal of the Canadian Chiropractic Association. 2014;58(3):320-327. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4139766/
Vitamin D Council. New survey highlights the need for increased awareness and knowledge of vitamin D. October 31, 2014. https://www.vitamindcouncil.org/vitamin-d-news/new-survey-highlights-the-need-for-increased-awareness-and-knowledge-of-vitamin-d/