Again, I think (I'm not a doctor of course, but what do they know.. :-)) as long as you eat enough fresh plant based food (you said you eat a lot of spinach for example), you will probably not be calcium deficient. And I don't think people need algae pills to get the calcium they need. In fact, I don't think vitamin pills are necessary at all, if you eat the right food.
Here is a cool video about "the leading causes of death": http://www.youtube.com/watch?v=30gEiweaAVQ
If I remember correctly, he also talks about stuff like osteoporisis (and how the number of people suffering of it is way higher in countries that eat a lot of dairy compared to countries that eat very little or not dairy).