Tuesday, 31 May 2011

Calcium

Most people of my generation who went to school in the UK during the 1970s-1980s will perhaps remember what I am about to describe. Picture this. You are 7 or 8 years old. You sit at one of a number of large tables in a school dining hall filled with all your school-mates. Everyone is chattering and talking about yesterdays TV episode of Rentaghost or the revelation that Darth Vader is Luke's father - 'your destiny lies with me Skywalker'. Then from out of nowhere a large tray arrives filled with third-of-a-pint bottles of milk with a straw in them. You all look apprehensively at each other and the bottles of milk, noting that the cream at the top of the milk seems to travel about a third of a way down the bottle. You touch the bottle - it is warm; 'warm' you say to your friends. The word gets passed down the table, 'it's warm'. You pick up the bottle and straw... 'be brave' you say to yourself and then down the hatch. At the time I never understood why we were made to drink these warm bottles of milk everyday at school. I say 'warm' but the only reason they were warm is because they had been stood out all morning awaiting their fate. It was only when I was old enough to read up about milk and calcium (and 'Thatcher, Thatcher milk snatcher') that I understood the true reasons. One of the reasons was calcium.

Calcium is pretty important for human health. I would be here all night if I was to list all of its known functions in relation to health and disease. Suffice to say calcium has a role to play in things like bone health and the correct functioning of various enzymes and other biological processes. There is still some debate on how much is required but generally speaking, the figures look like this (see page 265) and vary between 525 mg/day for infants up to 1000mg /day for adolescents. Adults are suggested to take in about 700 mg/day (assuming they are not lactating women where greater intake might be required).

Whilst milk and dairy products are quite a good source of calcium, it is by no means the only source of calcium. Foods such as sardines, sesame seeds, figs and spinach (all the things that children love - not!) also rank up there with milk. Added to the fact that many products such as bread and breakfast cereals are now fortified with calcium and other nutrients means that everyone should be able to get their recommended daily intake with pretty minimal effort from diet. Where there is some indication that dietary needs may not meet required calcium intake, there are a variety of supplements on the market to use.

I think that covers the basics of calcium; now on to some of the important details and debates. There is already recognition that calcium on its own is an important mineral. In recent years, that recognition has however given way to the concept of synergy, where other components are also required to give something that 'va-va voom'. For calcium it is vitamin D.

Most people will probably have heard of vitamin D - if only they have heard of what happens when you don't get enough - rickets. It is slightly disturbing to see that rickets might be making an unwelcome return here in the UK and across the developed world perhaps as a function of our diets, our increasingly sedentary lifestyles and our guidelines for sun protection. The so-called 'sunshine vitamin' is pretty important when it comes to calcium and ensuring that it is properly absorbed from the gut via calcitriol. I talked briefly about calcium supplementation. There are various conditions where calcium supplementation (and vitamin D) might be a requirement, particularly in bone conditions such as osteoporosis. Research also seems to suggest that other conditions might benefit from calcium supplementation including hypertension and a possible reduction of the risk of some cancers (although the effect is not magnificent).

There is however a potential downside to calcium supplementation which came from this study. Bolland and colleagues (2010) conducted a meta-analysis of 11 trials of calcium supplementation (alone) in women aged 40 years and above, and concluded that the data implied an elevated risk for adverse events such as myocardial infarction (alongside a non-significant risk for stroke and early mortality). Quite a lot of discussion and media coverage has followed this review paper, not least because of the findings relating to calcium supplementation alone without accompanying vitamin D. A more recent analysis (2011) here from by the same authors suggested that even where calcium and vitamin D were administered, there remained an increased risk of myocardial infarction or stroke in this population. Whether the results can be extrapolated outside of women over 40 years old remains unknown.

Getting back to my particular interest in calcium in relation to autism and various gastrointestinal disorders, there are some final notes to make. In a recent post I talked about osteopontin in relation to autism. In that post I touched upon a study conducted by Hediger and colleagues which reported reduced bone thickness as being present in autism and specifically in those cases where a casein-free diet was being followed. The authors recommended that monitoring be put in place for this at-risk group. Based on these results and general dietetic advice where casein (dairy products) is being removed from the diet, there is perhaps some assumption that calcium and vitamin D supplement may be indicated.

Another point to arise from the Hediger paper was that their results might also indicate some GI disorder or lack of sunlight exposure (p.854) as also accounting for their results. Sunlight exposure has already been mentioned. The GI disorder suggestion stems from work in coeliac disease where absorption problems associated with gut pathology place affected individuals at greater risk of low calcium (and vitamin D) levels which tend to normalise when a gluten-free diet in implemented. Bone health can surprising also be aided by such a diet in certain cases. The logic: your gut is more permeable than it should be in coeliac disease hence you do not absorb your vitamins and minerals properly. Cutting out gluten helps to decrease permeability (and other things) which means you absorb more from your diet. I do wonder if this might also be the case with the gut hyperpermeability (leaky gut) problems detailed in autism?

One final word on calcium and autism relates to the issue of chelation. From the outset I will say that I am not an expert on chelation for the removal of heavy metals and offer no opinion on effect or not. From my limited understanding, various chelating agents have been suggested to remove an excessive metal burden thought to be associated with some cases of autism, although at the current time very limited evidence of effect or safety has been published. Having heard about a very sad story about fatality linked to chelation therapy for autism I chanced upon this article reporting the facts of the case. Calcium is a metal and hence potentially susceptible to some forms of chelating agent (EDTA) resulting in hypocalcaemia.

So there you have it. I hark back to my opening memories of warm milk and school-days; all with the best intentions as 'be brave' is whispered under my breath.