> If we need about 1500 mg of calcium/day.(BTW where did this # come
> from?-seems they keep raising it every few years)

1500 mg of calcium/day is higher, sometimes much higher, than any on-line
source I consulted.  Most of these sources overestimate calcium requirements
and underestimate other bone-building nutrients (protein, vitamin D3,
magnesium, hormones, exercise, physical work, trace minerals...)

Dr. Cordain estimates the magnesium intake of early man to have been as much
as 800 to 1,500
mg per day, about equal to the estimated daily calcium intake, giving early
humans a calcium-to-magnesium ratio of about 1:1.

" In pre-agricultural diets consisting of meats, fruits, vegetables, nuts,
etc., the calcium (Ca) to magnesium (Mg) ratio is approximately 1:1. Because
the Ca:Mg ratio of milk and dairy products is 12:1, the inclusion of milk
and milk products into post-agricultural diets can raise the overall dietary
Ca:Mg ratio to 3 to 4:1 [Varo 1974]. In animal models, it has been shown
that rats develop clinical signs of magnesium deficiency after three weeks
on high-calcium, normal-magnesium diets [Evans and Weaver 1990; Luft et al.
1988; Sellig et al. 1974].

Ironically, high-calcium diets may have a deleterious effect upon bone
mineralization because of their hypomagnesic (magnesium-depleting) effect.
Conversely, magnesium deficiency is a known cause of hypocalcemia (low
calcium) [Rude et al. 1976]. (In other words, for either calcium or
magnesium utilization to be optimum, both must be in balance with each
other.) The resultant hypocalcemia stems from parathyroid hormone (PTH)
unresponsiveness [Rude et al. 1978], since the effects of PTH are
magnesium-dependent [Estep et al. 1969]."
sourec: www.beyondveg.com/cordain-l/prot-calc/prot-calcium-loss-1a.shtml

> Where did our paleo ancestors get enough without supplements?

Nuts and seeds.  Drinking water is also an important source, however surface
waters vary in their concentrations of calcium and magnesium (depends on its
contact with soil or rock, such as that found in groundwater).

> Currently I supplement with 500 mg of calcium citrate and 250 mg magnesium
> citrate because I fear I am not getting enough calcium and magnesium in my
> diet although I eat some form of leafy green vegetables daily and sardines
> 3-4 times per week.

A 1:1 ratio supplement would be better.  If you're not eating diary, you're
closer to a 1:1 ratio now.  The Eades recommend an *optional* 300mg of
calcium/day, while consuming 400 mg of magnesium/day (600 mg/day for anyone
with heart disease or diabetes).

> Can anyone estimate how much sardines/ leafy greens we need to consume to
> reach 1500 mg of calcium (and magnesium, for that matter)

sardines (3 oz) - 367 mg calcium

Evil GlaxoSmithKline www.calciuminfo.com/index.htm has an interesting
calcium calculator.  You can enter all the foods you normally eat, and your
total calcium intake is estimated.  A graph below the calculator plots
recommended levels (a 1000 mg/day is estimated for persons between 20 - 50
years of age; above 50 years of age, recommended daily intake increases to
1200 mg/day).  Not surprisingly, GlaxoSmithKline (wash my mouth out after
saying that word) recommends calcium-fortified TUMS where a deficiency is
indicated.  Sick!

Rob