While walking the dog today, my mind wandered and I found myself thinking about nutrient absorption. I’d just had lunch (leftover roast pork from yesterday) and some veggies and salad including rocket (a type of lettuce). My girlfriend dished it up and all I had to do was add a drizzle of olive oil to the rocket before serving. I like the taste and texture of olive oil on salad leaves. However, there is another reason for adding oil to salad – it enhances the absorption of so-called carotenoid nutrients. See here for more on this.

Thinking about this as I walked the dog got me thinking about other nutrients. If someone supplements with nutrients, say, what factors might affect absorption? I generally advise individuals who take vitamin and mineral supplements to take them with food. My rationale is that supplements are more likely to be ‘digested’ and nutrients absorbed when the digestive tract is in the throes of digesting and absorbing food. It suddenly occurred to me to look to see if there was any research on this.

A cursory search of the literature did not immediately reveal anything noteworthy regarding the absorption of nutrients generally, but I did find one interesting study that caught my eye. It concerned the absorption of one particular nutrient – vitamin D [1]. It piqued my interest partly because vitamin D appears to be such an important nutrient. But also, I’m taking it myself, in an effort to optimise my vitamin D levels.

This study focused on a group of individuals who were taking 1000 – 50,000 IUs of vitamin D (that’s not a typo, this upper dose is indeed fifty thousand IUs) each day as part of the medical management advised at a bone clinic in the US. Mean levels of vitamin D at the start of the study were 30.5 ng/ml (76 nmol/l). This level of vitamin D would generally be considered ‘sub-optimal’.

In an effort to boost absorption of vitamin D, individuals were asked to take their vitamin D supplements with the largest meal of the day. After 2-3 months, vitamin D levels were checked again.

At the end of the study period, vitamin D levels had risen to an average of 47.2 ng/ml (118 nmol/l) – an average increase in vitamin D levels of about 57 per cent.

This study is somewhat hampered by the fact that it lacked a control group – in this case a group of individuals who continued to take their vitamin D ‘normally’ (not, explicitly, at the biggest meal of the day). It’s possible, for instance, that the individuals in this study got, say, more sun exposure during the study and it is this that accounted for the rise in vitamin D levels.

Nevertheless, it seems sensible, I think, for individuals who are currently supplementing with vitamin D to take this with their largest evening meal. It doesn’t cost anything, and may provide supplementers with more bang for their buck.

References:

1. Mulligan GB, et al. Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25-hydroxyvitamin D. J Bone Miner Res. 8th February 2010 [epud ahead of print publication]